II-VI compounds: generally, compounds formed by elements from II & VI groups of the Periodic table. Here we mean only binary (ZnSe, ZnS, ZnTe (also for terahertz applications), CdSe, CdS, CdTe) and ternary (like, e. g., CdZnTe or CdSSe) zinc and cadmium chalcogenides that are wide-gap semiconductors.
     Semiconductor single crystals of CdxZn1-xTe (CdZnTe, CZT, Cadmium Zinc Telluride) are important materials for the development of far-infrared, visible light, X-ray detectors, and gamma-ray detectors as medical imaging devices. CdZnTe (CZT, Cadmium Zinc Telluride) radiation detectors have the advantages of a large absorption coefficient, compact size and room temperature operation. Currently used high purity Ge and Si detectors in industry and medical imaging can only work efficiently at the liquid-nitrogen temperature.
     There are many examples of the use of CZT (CdZnTe, Cadmium Zinc Telluride) detectors in medical imaging and diagnostics, ranging from simple x-rays carried out in a dentistís office to cardiac angiography, bone densitometry measurements, and the use of nuclear medicine to pinpoint areas of activity within the brain to help characterize conditions such as epilepsy. In addition, the medical imaging community is interested in developing large area CdZnTe (CZT, Cadmium Zinc Telluride) detector arrays.
     Cadmium zinc telluride (CdZnTe) has become a key detector technology for hard x-ray and gamma ray astronomy. Astronomers use CZT (CdZnTe, Cadmium Zinc Telluride) arrays to study the origin of high-energy gamma-ray bursts. One class of astronomy instruments will use large area single focal plane array detectors in conjunction with a focusing optic. CZT (CdZnTe, Cadmium Zinc Telluride) is also suited for high-resolution measurements and isotope identification in the nuclear industry and for x-ray radiography applications. The use of single crystal CZT (CdZnTe, Cadmium Zinc Telluride) as the gamma ray detector material has allowed the production of very compact prototype imaging systems. Further applications for CZT (CdZnTe, Cadmium Zinc Telluride) gamma ray detectors include space flight gamma burst instruments , high-energy x-ray astronomy, and international nuclear inspection and safeguarding.

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     Gallium Phosphide(GaP) has an energy band gap (EG) that can emit visible light, but it is an indirect gap semiconductor. It is combined with GaAs to produce GaAs1-xPx alloy which is both direct and has a light producing energy band gap (EG) for a 0.28 ≤ x ≤ 0.45 GaP is also used in manufacturing light-emitting diodes (LEDs). It can emit green light.
     InP wafers are attracting much attention as a key component in optical fiber communications equipment. Specifically, the semi-insulating InP mirror wafer is expected to become the mainstream material for photodiodes used in a high-speed communications system with a transmission speed of 40 Gbps or higher. Demand for InP is also expected to grow for use in the next-generation mobile phones, which require communications with higher speed and larger capacity.

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APPLICATIONS:
    • Generation second harmonics on CO and CO2 - lasers
    • Optical parametric oscilator
    • Different frequency generator to middle infrared regions up to 12 mkm.
    • Frequency mixing in the middle IR region from 4.0 to 18.3 µm
    • Tuneable solid state lasers (OPO pumped by Nd:YAG and others lasers operating in 1200 to 10000 nm region with efficiency 0.1 to 10 %)
    • Optical narrow-band filters in the region near isotropic point (0.4974 m at 300 °K), transmission band being tuned at temperature variation
    • Up-conversion of CO2 laser radiation image into near-IR or visible region by using/ or use of Nd:YAG, ruby or dye lasers with efficiency up to 30 %

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APPLICATIONS:
    • Generation second harmonics on CO and CO2 - lasers
    • Optical parametric oscilator
    • Different frequency generator to middle infrared regions up to 17 mkm.
    • Frequency mixing in the middle IR region

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      Chrysoberyl (BeAl2O4) modification - Alexandrite (Cr+3:BeAl2O4) is a particularly attractive precious gem. It is also a uniquely versatile solid-state laser material. It has the distinction of being the first solid-state laser medium capable of tunable operation at room temperature.
Alexandrite lasers are vibronic lasers; that is, phonons, as well as photons, are emitted during lasing. The wavelength tuning is accomplished by controlling the branching of energy between phonons and photons during lasing. Alexandrite lasers have been tuned across most of the spectrum between 701 and 860 nm. The central part of the tuning range is from 720 - 800 nm. Using non-linear wavelength conversion processes such as harmonic generation and raman shifting, light has been generated at wavelengths from the deep IR (20 µm) to the VUV.
      In addition to its broad absorption bands throughout the visible spectrum, alexandrite exhibits narrow R line absorption features at wavelengths near 680 nm. These properties together with its long fluorescence lifetime make it an excellent material for both flashlamp and diode pumping. Alexandrite's thermo-mechanical properties make it an excellent performer in high power laser applications.

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      Anti-Stokes Phosphors are developed for up-conversion of long-wave IR-radiation (1,5-1,6 um) into that short-wave (0,8-1,02 um) and radiation of IR-range 0,9-1,07 um into visible light of various colours. They are useful in night viewing devices for spectral sensitivity broadening of electron-optical image converters (upto 1,6 um), in light-emitting diodes (LED) of various types, for visualization IR-radiation and laser adjustment, as well as for marking of documents and value papers.
      The Phosphors of ASP-group are powders, consisting of rare earth activated compounds based on yttrium (and some other elements) oxides, fluorides, oxysulphides, oxychlorldes.
      The phosphors provide parameters stability of emitters during > 100000 hours and within temperature range -60°C +70°C.

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APPLICATIONS:
    • For harmonic generation (SHG, THG, 4HG, 5HG) of Nd:YAG laser, SHG, THG of Ti: Sapphire, Alexandrite lasers
    • For tunable solid state lasers using OPO (pumped by 355, 532 or 1064 nm)
    • For UV sources from SHG, SFG of dye lasers
    • For autocorrelation (in thin plates) in shortpulse (ps and fs) lasers

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      Alkaline Metals Biphthalate single crystals are used in x-ray spectral analysis as analysing crystals in a long wave spectral area. The analysing crystals serve to separate the X-radiation into spectrum. The usage of these crystals enables a qualitative and quantitative analysis of light elements (Fe, Al, Mg, F, Si), due to their lattice (up to 2.6 nm). The plasticity and high fissionability of these crystals facilitates the production of fine plates (0.2 - 0.5 mm) for focusing analyzers. Biphthalate crystals are stable in a vacuum.

            Potassium Biphthalate       KAP     C6H4(COOH)(COOK)
            Cesium Biphthalate        CsAP     C6H4(COOH)(COOCs)
            Rubidium Biphthalate       RbAP     C6H4(COOH)(COORb)
            Ammonium Biphthalate       NH4AP     C6H4(COOH)(COONH4)

      By increasing the cation radius, the reflection integral coefficient increases as well. Therefore these crystals, as for example CsAP, could be effectively used for qualitative x-ray spectral analysis of various materials and for overall spectra of remote astrophysical objects obtainment.
      By decreasing the cation radius, the resolving capacity of the method increases. The usage of such crystals, as for example NH4AP, as analysing crystals in x-ray spectrometers enables substantial extension of their resolving capacity in 0.8 - 2.5 nm.

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      The division of light into two components (an "ordinary" and an "extraordinary ray" ), found in materials which have two different indices of refraction in different directions (i.e., when light entering certain transparent materials, such as calcite, splits into two beams which travel at different speeds). Birefringence is also known as double refraction. Crystals possessing birefringence include hexagonal (such as calcite), tetragonal, and trigonal crystal classes exhibit birefringence, and are known as uniaxial. Orthorhombic, monoclinic, triclinic exhibit three indices of refraction. They are therefore trirefringent and are known as biaxial. Birefringent prisms include the Nicol prism, Glan-Foucault prism, Glan-Thompson prism, and Wollaston prism.
      Another material, an excellent birefringence optical crystal undoped YVO4 is developed newly. It has very good transmission in a wide wavelength range from visible to infrared, large index of refractivity and birefringence difference. Compared with other important birefringence crystals, YVO4 has higher hardness, better fabrication property, water insoluble and man-made than calcite (CaCO3 single crystal); easier to get large, high quality crystal and lower cost than rutile (TiO2 single crystal). Those outstanding properties make YVO4 very important birefringence optical material and widely used in opto-electronic research, development and industry. For example, the optical communication system needs a huge quantity devices of undoped YVO4, such as fiber optical isolators, circulators, beam displacers, Glan polarizers and other polarizing devices.

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      Sodium Chloride (NaCl) is used for windows, lenses and prisms where transmission in the 0.25 - 16 µm range is desired. Because of its low absorption, Sodium Chloride is being used in high power laser systems. Polished surfaces must be protected from moisture by exposing to only dry atmosphere or by using a heating element to maintain the Sodium Chloride above the ambient temperature. Sodium Chloride can be used up to 400°C. The material is sensitive to thermal shock. Irradiation generates color centers.
      Potassium Chloride (KCl) is used for infrared windows, lenses and prisms when transmission in the 0.3 - 20 µm range is desired (transmission extends beyond that of Sodium Chloride). Potassium Chloride is soluble in water and polished surfaces must be protected from moisture. Maximum use temperature is 400°C.
      Potassium Bromide (KBr) is used as IR spectroscopic components, beamsplitters, for CO2 -lasers. KBr is water soluble and must be protected against moisture degradation of polished surfaces. The material cleaves readily, and can be used at temperature up to 300 °C. Irradiation of KBr produces color centers.
      Cesium Iodide (CsI) is useful for infrared having transmission through the visible out to 70 µm in a 2 mm thickness. It is principally used for infrared prisms, cell w indows and as a beamsplitter or as interferometer plates. Cesium Iodide is also furnished as Thallium activated Cesium Iodide for scintillation crystals. Being relatively soft, this material has found application in satellite-borne radiation detectors, which must withstand extreme shock and vibration along with rapid temperature changes. Cesium Iodide precipitated powders are used in solid phase pelleting of samples for infrared spectroscopy. Cesium Iodide is highly water soluble and polished faces of this material may be damaged by moisture in the atmosphere when relative humidity is higher than 35%. CsI can be cut with a band saw. Standard polishing techniques can be used.

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APPLICATIONS:
    • generation highest harmonics (SHG, THG, 4HG, 5HG) of laser radiation YAG : Nd3+
    • generation second, third lasers harmonics on the alexandrite, Ti:sapphire

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     The Physical Vapor Deposition (PVD) materials - CHALCOGENIDES are useful as basic materials for production by thermal evaporation of transparent thin-film coatings, which improve the optical characteristics of workpieces made of glass, quartz, single crystals, semiconductors, etc.
     Used for deposition of mono- and multilayer optical coatings, they are effective in ultraviolet, visible and infrared spectral regions. Semiconductive properties of chalcogenide materials stipulate their application for interference optics in spectral region corresponding to energies lower than energy gap.
     Antireflective (AR) coatings reduce reflections and ghost images while enhancing the transmission of light. This is especially important when a large number of surfaces are used, as in microscopes, camera lenses or endoscopes. Besides antireflective coatings, a wide range of applications are served in the UV, visible and infrared range, in lighting systems, laser technology, projection systems, and even in medical applications such as mirrors, band-pass filters for information technology, coatings for displays, and more.
     The CHALCOGENIDE film-forming materials are deliverable in the form of tablets or granules, based on high-pure metal compounds. PVD processing is carried out in high vacuum at temperatures between 150 and 500 °C.

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     The HALIDES are useful as starting materials for production by thermal evaporation of transparent thin-film interference coatings, which improve the optical characteristics of workpieces made of glass, quartz, single crystals, semiconductors, etc.
     Used for deposition of mono- and multilayer optical coatings, they are effective in ultraviolet, visible and infrared spectral regions. Halides, fluorides in particular, is the most early class of film-forming materials, used as one of the first as thin-film dielectric antireflecting coatings in optics.
     Antireflective (AR) coatings reduce reflections and ghost images while enhancing the transmission of light. This is especially important when a large number of surfaces are used, as in microscopes, camera lenses or endoscopes. Besides antireflective coatings, a wide range of applications are served in the UV, visible and infrared range, in lighting systems, laser technology, projection systems, and even in medical applications such as mirrors, band-pass filters for information technology, conductive coatings for avionics displays, and more.
     The FLUORIDE film-forming materials are deliverable in the form of tablets or granules, based on high-pure fluorides of alkali, alkali-earth and other metal compounds, and in case of cesium iodide in form of boules. PVD processing is carried out in high vacuum at temperatures between 150 and 500 °C.

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     The Physical Vapor Deposition (PVD) materials - OXIDES are useful as basic materials for production by thermal evaporation, deposition by electron-beam or by ion-plasma evaporation of transparent thin-film coatings, which improve the optical characteristics of workpieces made of glass, quartz, single crystals, semiconductors, etc. Used for deposition of mono- and multilayer optical coatings, they are highly effective in ultraviolet, visible and infrared spectral regions.
     Antireflective (AR) coatings reduce reflections and ghost images while enhancing the transmission of light. This is especially important when a large number of surfaces are used, as in microscopes, camera lenses or endoscopes. Besides antireflective coatings, a wide range of applications are served in the UV, visible and infrared range, in lighting systems, laser technology, projection systems, and even in medical applications such as mirrors, band-pass filters for information technology, coatings for displays, and more.
     The OXIDES film-forming materials are deliverable in form of tablets or granules, based on high-pure metal compounds. PVD processing is carried out in high vacuum at temperatures between 150 and 500 °C.

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      Laser crystal Cr+4:Y3Al5O12 or Cr+4:YAG - is a material that can be used as an active media for CW, pulsed or self mode-locked tunable NIR solid-state lasers with the tunability range of 1340 - 1580 nm as well as a media for Q-switching in lasers with operating wavelength at 950 - 1100 nm. It is particularly useful in practical applications because of convenient absorption band of Cr+4 around 1 mm which gives possibilities to pump it by regular Nd:YAG lasers. A saturation of absorption in the band at 1060 nm is useful for application in small sized Nd:YAG oscillators with flash lamp or laser diode pumping instead of based on dye or LiF:F-center passive Q-switches. With the usage of Cr+4:YAG crystal the self mode-locking (KML) regime is achievable. It gives an opportunity to build the laser source with pulse duration shorter than 100 fs at 1450 - 1580 nm.
      Finally, its high thermal and radiation stability as well as excellent optical and mechanical properties will give you an opportunity to design reliable devices based on the crystal.

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      Due to significant absorption in the near infrared in pure L-arginine phosphate monohydrate (LAP) deuterated LAP ((DLAP) crystals have been grown using heavy water (D2O) as a solvent by a slow cooling technique. The growth conditions for the growth of monoclinic dLAP crystals are optimized by adjusting the growth parameters, such as pH, temperature etc. The grown crystals are morphologically compared with the pure LAP crystals. Deuterated L-arginine phosphate C6D14N4O2 · D3PO4 is a promising non-linear optical material having good non-linear coefficient, high damage threshold as compared to L-arginine phosphate(LAP) and potassium dihydrogen phosphate (KDP).

APPLICATIONS:
    • Second, third and fourth harmonic generation from the fundamental radiation 1.06 µm
    • Sum and difference frequencies generation in wide spectral range from UV to IR
Literature:
    • A.S. Haja Hameeda, G. Ravia, R. Ilangovana, A. Nixon Azariaha, P. Ramasamyb. Growth and characterization of deuterated analog of l-arginine phosphate single crystals. Journal of Crystal Growth 237–239 (2002) 890–893
    • Atsushi Yokotani, Takatomo Sasaki, Kunio Yoshida, and Sadao Nakai. Extremely high damage threshold of a new nonlinear crystal L-arginine phosphate and its deuterium compound. Appl. Phys. Lett. 55(26) 2692 (25 Dec 1989)

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The Faraday or Magneto-Optic Effect
     In 1845 Michael Faraday discovered that when a block of glass is subjected to a strong magnetic field, it becomes optically active. When plane-polarized light is sent through glass in a direction parallel to the applied magnetic field, the plane of vibration is rotated. Since Faraday's early discovery the phenomenon has been observed in many solids, liquids, and gases. The amount of rotation observed for any given substance is found by experiment to be proportional to the field strength and to the distance the light travels through the medium.
     The constant, called the Verdet constant, is defined as the rotation per unit path per unit field strength. In gases the density must also be specified.
Unlike the electro-optic effect, the magneto-optic effect causes a true rotation of the plane of polarization for any input polarization angle. In a simple electro-optic device, only pure rotations are available; all other intermediate voltages produce different degrees of elliptical polarization states from a linear input state. A Faraday rotator however will truly rotate the plane of input polarization through any angle (providing you can provide a strong enough magnetic field).
     The verdet constant for most materials is extremely small and is wavelength dependent. The effect is at its strongest in those substances containing paramagnetic ions such as terbium. The highest verdet constants are in fact found in terbium doped glasses.Although expensive, this material has significant benefits and other substrates, notably excellent transparency, high optical quality,big size and high resistance to laser damage.
Although the Faraday effect is not itself chromatic, the verdet constant itself is quite strongly a function of wavelength. At 632.8 nm, the verdet constant for Faraday Rotator Glass is 0.329 - 0.37 whereas at 1064 nm, it has fallen to 0.108. This behavior means that the devices manufactured with a certain degree of rotation at one wavelength, will produce much less rotation at longer wavelengths.
     Faraday Isolator. The most common application for a Faraday rotator is when coupled with input and output polarizers to form an isolator. At high power optical feedback can damage or disrupt the operation of femtosecond laser systems. To reduce this feedback an optical isolator based on the Faraday Effect is inserted into the system. Faraday Isolators are passive unidirectional, non reciprocal devices that utilize the phenomenon of Magneto-Optic Rotation to isolate the source from reflections in an optical system. The isolator protects the laser oscillator from optical feedback making Faraday Isolators a key component in many of today's laser systems.
     Faraday Rotators are also used for example in ring laser systems to introduce a loss mechanism (in conjunction with some other intra-cavity polarization selective element) which is greater for one direction of propagation than for the other.

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      Optical crystals, such as CaF2, BaF2, MgF2, LiF, NaCl, KCl, KBr, etc, are widely used in IR optics and UV optics. High transparency and low loss optical windows, prisms, lenses, achromatic lenses and parallel planes have been fabricated in these optical materials.
      Lithium fluoride (LiF) crystals suit well for manufacturing optical elements (mirrors, windows, lenses) for UV, visible and IR applications. These crystals are optically isotropic, middle hard, hygroscopic, unsolvable in water.
      Magnesium Fluoride (MgF2) is the only optical material combining wide spectral transmittance band with birefringince phenomenon and satisfactory thermal expansion coefficient for isotropic crosssection. It is used for UV-radiation sources and receivers windows manufacture; for optical elements of interference-polarization filters, as laser resonator optics elements in quantum electronics and as active material in IR and submillimeter band .
      Calcium Fluoride (CaF2 or Fluorite) crystals are transparent in wide spectrum band. The product finds use in windows, lenses operating in UV and IR spectrum band. Laser Use: Calcium Fluoride is also used as a host lattice for laser crystals. Due to its composition CaF2 has a much longer useful life than most materials when used in fluorine environment.
      Barium Fluoride (BaF2) crystals are transparent in wide spectrum band. The product finds use in windows, lenses of special types of objectives, as mirrors substrate in optical systems operating in UV and IR spectrum band.

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      Cr:Forsterite (Cr:Mg2SiO4) crystal is a new tunable laser material that fills the spectral void in the near-IR region. The tuning range covers the important spectral range from 1130 to 1348 nm, which provides a minimal dispersion in optical fibers. The Cr:Forsterite laser eventually explores its niche applications for semiconductor characterisation, eye-safe ranging, medical, industrial and scientific research. Both pulsed and continuous-wave (CW) laser operations have been obtained when pumped with 532, 578, 629 and 1064 nm.

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      Another material, which is very suitable for SHG in the mid-IR is Gallium Selenide (GaSe) non-linear optical single crystal, combining a large non-linear coefficient, a high damage threshold and a wide transparency range. The frequency-doubling properties of GaSe were studied in the wavelength range between 6.0 µm and 12.0 µm. GaSe has been successfully used for efficient SHG of CO2 laser (up to 9% conversion); for SHG of pulsed CO, CO2 and chemical DF-laser (l = 2.36 µm) radiation; upconversion of CO and CO2 laser radiation into the visible range; infrared pulses generation via difference frequency mixing of Neodymium and infrared dye laser or (F-)-centre laser pulses; OPG light generation within 3.5–18 µm; terahertz (T-rays) radiation generation. It is impossibile to cut crystals for certain phase matching angles because of material structure (cleave along (001) plane) limiting areas of applications.

Literature:
    • Wei Shi, Yujie J. Ding, Nils Fernelius, Konstantin Vodopyanov. Efficient, tunable, and coherent 0.18 - 5.27-THz source based on GaSe crystal: erratum. Optics Letters, (2003) v. 28, 2, 136-136
    • R. A. Kaindl, F. Eickemeyer, M. Woerner, T. Elsaesser. Broadband phasematched difference frequency mixing of femtosecond pulses in GaSe: experiment and theory. Appl. Phys. Lett. 75 (1999) 1060-1062
    • K. L. Vodopyanov. Parametric generation of tunable infrared radiation in ZnGeP2 and GaSe pumped at 3 µm. JOSA B, 1993, 10, 9, 1723

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      Germanium (Ge) is most widely used for lenses and windows in IR systems operating in the 2 - 12 µm range. Enviroment does not make any problems because Germanium is inert, mechanically rugged, and fairly hard. It is an excellent choice for multi-spectral systems and for applications where EMI shielding is necessary. Germanium can be electrically heated for anti-fogging or anti-icing applications.
      Silicon (Si) is commonly used as a substrate material for infrared reflectors and windows in the 1.5 - 8 µm region. The strong absorption band at 9 µm makes it unsuitable for CO2-laser transmission applications but it is frequently used for laser mirrors because of its high thermal conductivity and low density. Silicon is also a usefull transmitter in the 20 µm range.

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     High values of laser damage threshold and conversion efficiency allow to use Mercury Thiogallate HgGa2S4 (HGS) non-linear crystals for frequency doubling and OPO/OPA in the wavelength range from 1.0 to 10 µm. It was established that SHG efficiency of CO2 laser radiation for 4 mm length HgGa2S4 element is about 10 % (pulse duration 30 ns, radiation power density 60 MW/cm2). The high conversion efficiency and wide range of radiation wavelength tuning allows to expect that this material may compete with AgGaS2, AgGaSe2, ZnGeP2 and GaSe crystals in spite of the considerable difficulty of big size crystals growth process.

APPLICATIONS:
   • Generation second harmonics on CO and CO2 - lasers
   • Different frequency generator to middle infrared regions.
   • Optical parametric oscilator
   • Frequency mixing in the middle IR region

Literature: F. Rotermund, V. Petrov and F. Noack, Difference-frequency generation of intense femtosecond pulses in the mid-IR (4-12 µm) using HgGa2S4 and AgGaS2. Opt. Commun. 185 (2000) 177-83

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      DKDP crystals can be supplied with a deuteration level of >94%, >96% and >98%.

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      Neodymium doped Potassium-Gadolinium Tungstate crystals (Nd:KGd(WO4)2 or Nd:KGW) are low-threshold high effective laser medium exceptionally suitable for laser rangefinders. The efficiency of such lasers is 3 - 5 times better than that of the Yttrium-Aluminium Garnet (YAG) lasers. At low pumping energies (0.5 to 1.0 J) KGW crystals are one of the few materials ensuing an effective generation. KGW single crystals can also be used for the fabrication of high-efficiency lasers with high output energy. The single crystals exhibit a high optical quality. KGW crystals have great value of the bulk strength for laser radiation. The technology enables the obtaining of KGW single crystals with the weight of up to 3 kg and fabrication of round active elements with the diameter from 4 to 12 mm and the length from 50 to 120 mm.
      Yb:KGW is one of the most promising laser active materials. The simple two-level electronic structure of the Yb ion avoids undesired loss processes such as upconversion, excited state absorption, and concentration quenching. Compared with the commonly used Nd:YAG crystal Yb:KGW crystal has a much larger absorption bandwidth, 3 or 4 times longer emission lifetime in similar hosts with enhanced storage capacity, lower quantum defect and is more suitable for diode pumping than the traditional Nd-doped systems. The smaller Stokes shift reduces heating and increases the laser efficiency. In comparison with other Yb doped laser crystals such as Yb:YAG and Yb:YCOB crystals, Yb:KGW has a much higher (13-17 times) cross-section of absorption, lower quantum defect (~4%), a cross-section of emission that is 9 times higher than Yb: YCOB, and emission band that is broader than Yb:YAG, a high nonlinear coefficient of refraction, and the highest slope efficiency (87%). With such performance advantages, Yb:KGW crystals are expected to replace Nd:YAG and Yb:YAG crystals in high-power diode-pumped laser systems. Yb:KGW also holds great promise for creating high-power, short pulse duration femtosecond lasers and their broad applications.
      The emission linewidth of KYW:Yb or KGdW:Yb is broader than in YAG and comparable to that in glasses. This linewidth is interesting not only for potential tuning but mainly for the generation and amplification of short (ps or fs) laser pulses. Mode-locking of a diode-pumped KGdW:Yb laser has been demonstrated and utilization of the crystal anisotropy for maximum gain bandwidth culminated in the generation of 71 fs pulses with KYW:Yb in 2001. Also, the first regenerative amplification of fs pulses in KYW:Yb has been demonstrated in 2001. Whereas fs pulses can provide ultimate peak powers, much higher average powers and optimum conditions for frequency conversion to other wavelengths can be realized with slightly longer pulses (1 ps or more for Raman conversion). The slope efficiency up to 78% was demonstrated with the Ti:Sapphire-laser and 66% with the diode laser pumping. This high value of the slope efficiency opens potential for further nonlinear optical conversion of this radiation with a good overall efficiency.

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      Thallium Halogenide crystals (KRS-5, KRS-6) are designed for transmission, refraction and focusing of visible and infrared radiation. Wide transparence range, radiation, thermal and vibrational stability, low water solubility make these crystals valuable for applications in optical devices working in atmosphere conditions and outer space without special protection. Low absorbtion in MID-IR and large refractive index make these crystals suitable for internal reflection elements.
      KRS-5 is used for attenuated total reflection prisms, IR windows and lenses where transmission in the 0.6 µm - 40 µm range is desired. It has a tendency to cold-flow and change its shape with time. KRS-5 is only slightly soluble in water but can be dissolved in alcohol, nitric acid, and aqua regia. KRS-5 (TlBr-TlI) is a gorgeous red crystal commonly used for attenuated total reflection prisms for IR spectroscopy. It is also used as an infrared transmission window in gas and liquid sample cells used with FTIR spectrophotometers in place of Potassium Bromide (KBr) or Cesium Iodide (CsI) for analysis of aqueous samples that would attack KBr or CsI optics. It has a wide transmission range and is virtually insoluble in water. It is a useful alternative to AgCl since it is not photo-sensitive and for ATR applications it will transmit well beyond the 18 micron useful range of ZnSe. KRS-5 is considered toxic, but in our opinion it is safe for IR spectroscopic applications when properly handled.

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APPLICATIONS:
    • Optical parametric oscilator in middle IR region 1 - 5.5mkm
    • Different frequency generator in middle IR region 1 - 5.5mkm.

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APPLICATIONS:
    • Second harmonic generator of radiation 1.064 µm
    • Optical parametric oscilator in near IR region up to 4 µm
    • Different frequency generator in near IR region

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APPLICATIONS:
    • SHG from high power lasers: Nd:YAG, Ti:Sapphire (650 - 1100 nm), Alexandrite (700 - 800 nm) and Copper-vapor (580 nm)
    • THG of YAG, Ti:Sapphire, Alexandrite lasers
    • Tunable solid-state lasers using UV (308, 355 nm), visible or IR (1064 nm) as the pump in OPO process
    • Phase atching cut off: at fundamental 554 nm for SHG, at 794 nm for THG, down to 160 nm for SFM
    • Autocorrelation measurements of ultrashort optical pulses

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      White light can be made different ways - by mixing reds, greens, and blues, by using an ultraviolet LED to stimulate a white phosphor (the same stuff that's inside a fluorescent bulb) or by using a blue-emitting diode that excites a yellow-emitting phosphor embedded in the epoxy dome. The combination of blue and yellow makes a white-emitting LED. Combine a white phosphor LED with a few amber ones, and you can create a range of different whites - from the romantic glow of a candle flame to the hot, bright light of the sun.
      Most "white" LEDs in production today use a 450nm – 470nm blue GaN (gallium nitride) LED covered by a yellowish phosphor coating usually made of cerium doped yttrium aluminium garnet (YAG:Ce) crystals which have been powdered and bound in a type of viscous adhesive. The LED chip emits blue light, part of which is converted to yellow by the YAG:Ce. The single crystal form of YAG:Ce is actually considered a scintillator rather than a phosphor. Since yellow light stimulates the red and green receptors of the eye, the resulting mix of blue and yellow light gives the appearance of white.
      White LEDs can also be made by coating near ultraviolet (NUV) emitting LEDs with a mixture of high efficiency europium based red and blue emitting phosphors plus green emitting copper and aluminium doped zinc sulfide (ZnS:Cu,Al).

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APPLICATIONS:
   • From second to forth harmonic generations of the fundamental laser emission in the range from 690 to 2000 nm
   • Optical parametric oscillation, obtaining of the tuned radiation in the ranges from 800 to 4000 nm
   • Frequency multiplication and mixing in transparency crystal range from 280 to 5500 nm
   • Measurement of parameters of ultra-short laser pulses including of the single ones
   • Visualisation of IR radiation to obtain the object image by non-linear optical methods

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      Non-linear characteristics of Lithium Thioindate (LiInS2 or LIS) crystal are close to AgGaS2 and AgGaSe2, but their crystal structures are different. LiInS2 is pyroelectric, its electrooptical parameters are the base for using it as an effective electrooptical material.
APPLICATIONS:
    • up-conversion of CO2-laser radiation image into near-IR or visible region • Different frequency generator in midle IR range (2-12 µm)
    • Optical parametric oscilator in 1-12 µm range with pump Al2O3: Ti • Frequency mixing in the middle IR region
    • For tunable solid state lasers using OPO, pumped by Nd:YAG and others lasers in range 1.2 - 10 µm

Literature:
    • L. Isaenko, A. Yelisseyev, S. Lobanov, A. Titov, V. Petrov, J.-J. Zondy, P. Krinitsin, A. Merkulov, V. Vedenyapin and J. Smirnova. Growth and properties of LiGaX2 (X=S, Se, Te) single crystals for nonlinear optical applications in the mid-IR. Cryst. Res. Technol. 38 (2003) 379-87
    • L. Isaenko, A. Yelisseyev, S. Lobanov, V. Petrov, F. Rotermund, G. Slekys and J.-J. Zondy. LiInSe2: A biaxial ternary chalcogenide crystal for nonlinear optical applications in the mid-infrared J. Appl. Phys. 91 (2002) 9475-80.
    • L. Isaenko, A. Yelisseyev, S. Lobanov, A. Panich, V. Vedenyapin, J. Smirnova, V. Petrov, J.-J. Zondy and G. Knippels. Characterization of LiInS2 and LiInSe2 single crystals for nonlinear optical applications. In Progress in Semiconductors Materials for Optoelectronic Applications 692 (2002) 429-34, E. D. Jones, M. O. Manasreh, K. D. Choquette et al. eds. (MRS, Warrendale, Penn, USA, 2002)
    • L. Isaenko, A. Yelisseyev, S. Lobanov, V. Petrov, F. Rotermund, J.-J. Zondy and G. H. M. Knippels. LiInS2: A new nonlinear crystal for the mid-IR. Mat. Sci. Semicond. Process. 4 (2001) 665-8.
    • F. Rotermund, V. Petrov, F. Noack, L. Isaenko, A.Yelisseyev and S. Lobanov. Optical parametric generation of femtosecond pulses up to 9 mm with LiInS2 pumped at 800 nm. Appl. Phys. Lett. 78 (2001) 2623-5.
    • G.M.H. Knippels, A.F.G. van der Meer et al, Mid-infrared (2.75-6.0-µm) second-harmonic generation in LiInS2, Optics Letters, May 1, 2001, 26,9, 617-619.

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      Lithium Niobate (LiNbO3 or LNB) and Lithium Tantalate (LiTaO3 or LTA) possess a combination of unique electro-optical, acoustic, piezoelectric, pyroelectric and non-linear optical properties making it a suitable material for applications in acoustic, electro-optical and non-linear optical devices, high-temperature acoustic transducers, receivers-transmitters of acoustic vibrations, air force acceleration meters, acoustic wave delay lines, deflectors, generators of non-linear distorted waves, acoustic filters, electro-optical Q-modulators (Q-switch), encoders-decoders, filters in television receivers, video-recorders and decoders, converters, frequency doublers and resonators in laser systems, non-linear elements in parametric light generators, etc. An indispensable condition of some of these applications is a high degree of optical uniformity of Lithium Niobate crystals used for fabrication of active elements. Crystal growth technology by low temperature-gradient Czochralsky method allows the growth of large-size high-quality LNB (up to 1-1.5 kg) and LTA single crystals for such non-conventional applications. It should be noted that both crystals are non-hygroscopic, colourless, water-insoluble and have low transmission losses.
      LiNbO3 damage due to photorefractive effect in congruent melt grown LiNbO3 certainly limits it's applications in high optical power devices. It is similar to the Li-rich VTE LiNbO3 with the obvious advantage that bulk samples can be obtained. Another possibility to increase laser damage threshold of LiNbO3 is doping with MgO.
      Some other crystals of LiNbO3 series are available, including LiNbO3 doped with Fe, Zn, Gd, Cu , Y, B, Er etc.
      For some applications similar in properties Lithium Tantalate (LiTaO3) crystal is more advantageous than LiNbO3 (E-O modulators, pyroelectric sensors etc.). Lithium Tantalate exhibits unique electro-optical, pyroelectric and piezoelectric properties combined with good mechanical and chemical stability and wide transparency range and high optical damage threshold. This makes LiTaO3 well-suited for numerous applications including electro-optical modulators, pyroelectric detectors, optical waveguide and SAW substrates, piezoelectric transducers etc.

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      Photoluminescent materials with long afterglow was developed as a base of non-radioactive luminescent paints used for various signs and directions, means providing safe traffic, marking of roads, important devices and control elements, microcrack and microdefect revealing (paste), wall painting, in art and polygraphy, office and shop window decoration etc., as well as a filler for plastics, films, artificial fibres, leathers, rubbers, textiles, ceramics and various articles on their base (e.g. clothes, bijouterie, toys, souvenirs, switches, special means for equipment of police, rock-savers and fire-brigades and other purposes).
      Sources of excitation of emission (fluorescence) these of photoluminescent materials may be daylight, luminescent and incandescent lamps, UV-emitters. They convert UV- and visible light into various coloured luminescent emission with afterglow duration from minutes to several hours.
      The phosphors can work within temperature range from -50°C to +1000°C and are stabile in different environment conditions.

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      Lithium Tetraborate (Li2B4O7 or LTB) has attracted much attention as a newly developed single crystal which has potential application to surface acoustic wave (SAW) devices. It is characterized by a low-temperature coefficient of the delay time, high electro-mechanical coupling constant and large piezoelectric constant.

APPLICATIONS:
    • Harmonic generation (SHG, THG, 4HG, 5HG) of YAG lasers
    • High power ultraviolet light source based on SHG and SFH of the visible laser radiation
    • In BAW and SAW devices

Literature:
    • V. Petrov, R. Komatsu and T. Sugawara. Temperature tuned noncritical phase-matching in Li2B4O7 for generation of cw laser radiation at 244 nm. Electron. Lett. 35 (1999) 721-2
    • R. Komatsu, T. Sugawara, N. Watanabe, S. Uda and V. Petrov. Growth and UV nonlinear properties of optical-grade lithium tetraborate (Li2B4O7) crystals. The Review of Laser Engineering 27 (1999) 541-6
    • V. Petrov, F. Rotermund, F. Noack, R. Komatsu, T. Sugawara and S. Uda. Vacuum ultraviolet application of Li2B4O7 crystals: generation of 100 fs- pulses down to 170 nm. J. Appl. Phys. 84 (1998) 5887-92

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     Crystals of group RE:MPb2X5 ( M=K, Rb X= Cl, Br) is a new promising active media for lasers, operating on different wavelengths in the range from UV to mid-IR, including those for TV amplifiers with diode pumping. Interest to this material, which has high RE segregation coefficients and a set of attractive properties increased considerably to date, while:
    • Low energy of phonons in halogenides provides mainly radiative transitions between adjacent levels with the gap = 1500 cm-1 as a result emission bands cover the wide spectral region from UV (transitions from upper excited levels) to 9-10 µm in the mid-IR (transitions within both excited and ground RE multiplets);
    • Complex of long decay times for lower states, high values of absorption cross-sections and low rates of the nonradiative multiphonon relaxation makes these crystals promising for their application as active media for UV/VIS lasers with up-conversion pumping;
    • Broad variations of RE type and dopant concentrations are possible for RE:MPb2X5 crystals;
    • Relatively broad, structureless luminescence bands in RE:MPb2X5 crystals allow fine tuning of the stimulated emission frequency;
    • To date stimulated emission has been obtained for 1.064 µm (Nd), 1.3 and 2.4 µm (Dy) and 4.6 µm (Er);
    • It is important that intense absorption bands match the laser diodes emission for many RE ions in MPb2X5 crystals.
Protective/antireflection coatings may be performed on the aperture surfaces of the produced elements. Typical sizes of optical elements are 4 x 4 x (5-15) mm3.

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      Phosphors for colour television
      Phosphors for colour display tubes
      Phosphors for black & white television and display tubes
      Low voltage cathodoluminescent phosphors for conventional VFD
      Low voltage cathodoluminescent phosphors for VFD of novel type
      Cathodoluminescent phosphors for projection
      Phosphors for electron-beam devices with high resolution
      Powdered electroluminescent materials
      Narrow-band lamp phosphors
      Phosphors for gas-discharge panels
      Thermoindicators of melting in temperature range from 117 to 2152°C
      Nothing of the above listet materials is interesting

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      Chromium-Ytterbium-Erbium activated glasses are designed for maximal efficiency (up to 2.5 - 3.0 % in free running) under Xe flash lamp pumping in the regime of rare pulses.
      Neodymium-Ytterbium-Erbium activated laser glasses are designed for efficient (up to 2.0 - 2.5 %) flashlamp pumped operation in case of repetitive pulses. Heat dissipation in them is lower than that in Chromium-containing glasses and they exhibit no temperature decrease of lasing parameters.
      Concentrated Ytterbium-Erbium phosphate laser glasses for laser diode pumped operation. Lasing wavelengths - 1.05 and 1.35 µm. These glasses have extremely high (4 x 1021 cm-3) Ytterbium ions content resulting in high absorption coefficient of InGaAs Laser diode radiation (up to 35 cm-1 at the peak at 975 nm). Erbium content can be varied depending on the customers demands (typically (3 - 5) x 1019 cm-3 for side pumping and (1.5 - 2) x 1020 cm-3 for microchip lasers). Availability - rods or plates according to customer's demands with appropriate antireflection or reflective coatings.
      Concentrated Nd phosphate glass with lowered concentration luminescence quenching. Lasing wavelengths - 1.05 and 1.35 µm.
      Erbium activated phosphate laser glass. Lasing wavelength - 1.54 µm

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     UV itself can be subdivided into near UV (380-200 nm wavelength) and extreme or vacuum UV (200-10 nm). When considering the effects of UV radiation on human health and the environment, the range of UV wavelengths is often subdivided into UV-A (380-315 nm)[also called Long Wave or "blacklight"], UV-B (315-280 nm)[also called Medium Wave], and UV-C (280-10 nm)[also called Short Wave or "germicidal"]. Unshielded exposure of the skin or eyes to mercury arc lamps that do not have a conversion phosphor is quite dangerous.
     The phosphors convert the ultraviolet radiation of mercury discharge of UV-C range (253,7 nm) into longer wavelength range UV-A. Such converted UV-light is applicable in medicine for phototherapy of skin diseases (in particular, psoriasis), in cosmetics for artificial sunburn, in photocopy equipment, for photopolymerization, UV-hardening, metal defectoscopy, for cheking up banknotes, for creating decorative-advertising effects in illumination and many other purposes.

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     The photorefractive effect is a phenomenon whereby the local index of refraction is modified by spatial variations of the light intensity. It is strongly observed when coherent rays interfere with each other in a photorefractive material which forms a spatially varying pattern of illumination. As a result, charge carriers are produced in the material which migrate owing to drift or diffusion and space charge separation effects. The resulting electric field that is produced induces a refractive index change via the electro-optic effect. Some of applications are: spatial light modulators, 4 wave mixing, phase conjugation, optical memory and computing.
     Sillenite single crystals Bi12SiO20 (BSO) and Bi12GeO20 (BGO) show unique combination of different physical properties. BSO and BGO crystals are very efficient photoconductors with low dark conductivity that allow to build up large photo-induced space-charges. Also strong spectral dependence of the photoconductivity and their electrooptic properties allow to develop and produce a wide range of optical device and systems. BSO and BGO crystals are used in spatial light modulators, dynamic real-time hologram recording devices, phase conjugation wave mixing, optical correlators, optical laser systems for adaptive correction of ultrashort light pulses. Photo-induced absorption make possible to develop and produce ô light-lightö type of optical devices such as optical modulators, switches etc. The fabrication Sillenite Oxide thin-film crystal structures by different technique permits the development of a long list of devices including optical waveguides, integrated optical devices. The use of waveguide optical structures based on Sillenites allows to achieve uniform illumination (normally to the plane of waveguide ) in a wide spectral range.
     The relatively large electrooptic and Faraday effect of Sillenite Oxides makes them useful for optical fiber electric/magnetic fields sensors.
     Strontium-Barium Niobate (SrxBa(1-x)Nb2O6) SBN is an excellent optical and photorefractive material. Nominally pure and doped by Ce, Cr, Co, Fe. SBN crystals of different compositions are used in elecro-optics, acousto-optics, photorefractive non-linear optics. A new growing technique provides excellent optical quality single crystals, free of growth striations, inclusions and other inhomogeneities, as well as definite cross section and linear dimensions up to 80mm. SBN crystalline elements meet the requirements for different applications. Based on this unique crystal growing technique, large high quality SBN optical elements and photorefractive cells are available.Fe:LiNbO3 (other dopants are available).
     Iron doped Lithium Niobate crystal (Fe:LiNbO3) is a kind of common used photorefractive materials with high electro-optical (EO) coefficients, high photorefractive sensitivity and diffraction efficiency. Compared to BaTiO3 series photorefractive crystals, it has some outstanding advantages, such as easy operation and storage, low cost and large size availability, which make it more suitable for volume fabrication and practical devices. Therefore, Fe:LiNbO3 crystal will forecast a wide range applications.

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      Non-linear organic single crystal 3-Methyl-4-Nitropyridine-1-Oxide (C6H6O3N2 or POM). The experimental data evidences that POM is a promising material for a pico- and femtosecond optics in the near IR: non-linear optical coefficient 15 times higher that of than KDP, small phase matching hall width (5 angular min /cm) and dispersion (0.5 angular min A). POM is biaxial positive crystal: 2V = 69° at 532 nm.

APPLICATIONS:
    • Second harmonic generation from low-energy and diode lasers with wavelength 1.06, 1.30 and 1.55 µm fundamental radiation
    • Parametric amplification and light generation in the range 0.8 - 2.0 µm
    • Correlation measurement of ultra-short laser pulse duration

Literature:
    • Boomadevi S.; Mittal H.P.; Dhansekaran R. Synthesis, crystal growth and characterization of 3-methyl 4-nitropyridine 1-oxide (POM) single crystals. Journal of Crystal Growth 15 January 2004, vol. 261, no. 1, pp. 55-62(8)
    • Rainer Glaser, Grace Shiahuy Chen. Electronic Structure Analysis of the Nonlinear Optical Materials 4-Nitro-pyridine N-oxide (NPO) and 3-Methyl-4-nitropyridine N-oxide (POM). Chem. Mater. 1997, 9, 28-35

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      Cr4+:Y3Al5O12 or Cr4+:YAG - is a material that can be used as an active media for CW, pulsed or self mode-locked tunable NIR solid-state lasers with tunability range 1340 - 1580 nm as well as a media for Q-switching in lasers with operating wavelength at 950 - 1100 nm. It is particularly useful in practical applications because of convenient absorption band of Cr4+around 1 mm which gives possibilities to pump it by regular Nd:YAG lasers. A saturation of absorption in the band at 1060 nm is useful for application in small sized Nd:YAG oscillators with flash lamp or laser diode pumping instead of based on dye or LiF:F-center passive Q-switches. Using the Cr4+:YAG crystal the self mode-locking (KML) regime is achievable. It gives an opportunity to build the laser source with pulse duration shorter then 100 fs at 1450 - 1580 nm. Finally, its high thermal and radiation stability as well as excellent optical and mechanical properties will give you an opportunity to design reliable devices based on the crystal.
      Gadolinium-scandium-gallium garnet doped with chromium and magnesium GSGG:Mg:Cr4+ is a material for passive Q-switching in 1 µm region. The valence state of chromium ion Cr4+ is provided by use of charge compensator. The crystals are grown by Zchochralski method in argon-oxigen atmosphere. Crystals of GSSS:Mg:Cr possessing the contrast parameter close to the one of YAG:Cr4+ have some advantages such as: possibility to provide necessary initial transmission at less thickness (typical thickness is about 1mm), transparency in the visible range which simplifies the alignment procedure.
      The crystals of Yttrium-Aluminum Garnet (YAG) doped with three-valence vanadium V3+ (V:YAG) in tetrahedral position suggest efficient q-switching for lasers operating in 1.3 µm region. The absorption band between 1.0 - 1.5 µm is attributed to 3A2 →3T2 transition of V3+ ion in tetrahedral position of garnet lattice. The crystals are grown by oriented crystallization method. Concentration of V3+ in tetrahedral position is controlled by growth and annealing conditions.The efficient q-switching of lasers operating at 1.3 micron has been obtained with a number of active mediums such as Nd:YAG, Nd:YVO4, Nd:KGd(WO4)2 under flash-lamp and laser diode pumping.
      Spinel crystal is a material having high optical damage threshold and low optical losses in 1.3 - 1.6 µm spectral range. Co2+-activated MgAl2O4 (Co:MALO, Co:spinel) can be used as a media for passive Q-switch of lasers which operate in the spectral range of 1.3 - 1.6 µm, for example 1.32 µm and 1.44 µm Nd:YAG lasers, 1.31 µm iodine lasers and especially 1.54 µm erbium glass lasers. High enough absorption cross-section of Co+2 ions together with practical absence of excited state absorption makes this material a very efficient passive Q-switcher (that does not require intracavity focusing) for various types of erbium glass lasers, including diode-pumped microchips.
      The new saturable absorber is based on NANOSIZED CRYSTALS IN GLASS MATRIX. It is transparent glass ceramics containing magnesium-aluminum spinel nanocrystallites doped with tetrahedrally coordinated Co2+ ions. The material provides q-switching within the spectral interval of 1200 - 1600 nm in particular for Yb-Er-glass laser (λ = 1.54 µm). Having the absorption cross-section of Co2+ at the wave length of 1.54 µm (transition 4A2 → 4T1(4F)) significantly higher than emission cross-section of Er:glass, it allows Q-switch operation without focusing radiation into the saturable absorber. In comparison with single crystals the glass ceramics is considerably cheaper. The glass ceramics technology is based on controlled nucleation and crystallization of the glass and has several advantages over conventional powder-processed ceramics as it uses glass preparation technique. They are: 1) ease of flexibility of forming in glassy state, 2) uniformity of microstructure, 3) reproducibility of properties that results from starting glass.

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      Crystal quartz (SiO2) is a very useful material for fabrication of finished optics: laser beamsplitters, AO elements, polarizing optics, prisms, windows, lenses in the ultraviolet because of its high UV, VIS and NIR transmittance, birefringence, ability to rotate plane polarized light, high damage threshold and resistance to scratching. The optical grade material is featured by highest possible transmittance throughout range 190 - 2900 nm, virtual freedom from bubbles and inclusions. Grown boules are Z - crystals and about 100 mm in the direction down optic axis that limits corresponding dimension in an optical part.
      Silicon dioxide occurs naturally as sand or rock and when melted, the resulting product is called Fused Quartz. If the silicon dioxide is synthetically derived, the material is often called Fused Silica. Fused Quartz is very pure, has a high chemical resistance, good thermal shock resistance and is very strong in compression. The low thermal expansion coefficient makes it ideal for mirrors and optical flats. It is used for viewing windows, being transparent to wavelengths from around 0.2 to 3.5 µm, insulators for electronic applications and for semi-conductor manufacturing.

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      When light encounters molecules in the air, the predominant mode of scattering is elastic scattering, called Rayleigh scattering. This scattering is responsible for the blue color of the sky; it increases with the fourth power of the frequency and is more effective at short wavelengths. It is also possible for the incident photons to interact with the molecules in such a way that energy is either gained or lost so that the scattered photons are shifted in frequency. Such inelastic scattering is called Raman scattering.
      New reliable preferably all solid-state sources of laser radiation in up-to-now uncovered spectral regions are highly desirable due to the growing number of applications of suchdevices in medicine, spectroscopy, defense, and research in general. Stimulated Raman scattering (SRS) in solid state crystals has been recently more widely employed for laser radiation frequency conversion. Use of solid state SRS converters is advantageous due tohigh conversion efficiency, no phase matching necessity, and easier handling comparing togaseous and liquid Raman cells. Among the most efficient known Raman crystals belong Ba(NO3)2 and KGd(WO4)2. New Raman-active crystal - BaWO4 - was recently predicted to be a promising Raman material suitable for a wide range of pumping pulse durationfrom picoseconds to nanoseconds.

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      Synthetic Sapphire is a single crystal form of corundum, Al2O3, also known as alpha-alumina, alumina, and single crystal Al2O3. Sapphire is aluminium oxide in purest form with no porosity or grain boundaries, making it theoretically dense. The combination of favourable chemical, electrical, mechanical, optical, surface, thermal, and durability properties make sapphire preferred material for high performance system and component designs. For various semiconductor applications sapphire is the best choice in the comparison with other synthetic single-crystals.
      Sapphire substrates / wafers: EPI-polished, optically polished, lapped or as-cut sapphire disks, windows, substrates, blanks as well as epitaxial structures “silicon-on-sapphire” (SOS)

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CRYSTALS
The technology for growing crystals made it possible to pull high-quality ingots of:
     - CWO - 60 mm in diameter and 150 mm long,      - NaI(Tl), CsI(Tl) and CsI(Na) - ingots (up to 100 mm in diameter and 250 mm long)
     - PWO - 30 mm in diameter and 250 mm long      - BGO - 75 mm in diameter and 150 mm long or 55 mm in diameter and 230 mm long
     - GSO - 55 mm in diameter and 180 mm long      - ZnSe(Te) - 25-40 mm in diameter and 120-150 mm long

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     Light output (LO) is the coefficient of conversion of ionizing radiation into light energy. Having the highest LO, NaI(Tl) crystal is the most popular scintillation material. Therefore, LO of NaI(Tl) is taken to be 100%. Light output of other scintillators is determined relative to that of NaI(Tl) (%). LO (Photon/MeV) is the number of visible photons produced in the bulk of scintillator under gamma radiation.
     Scintillation Decay time is the time required for scintillation emission to decrease to e-1 of its maximum.
     Energy resolution is the full width of distribution, measured at half of its maximum (FWHM), divided by the number of peak channel, and multiplied by 100. Usually Energy resolution is determined by using a 137Cs source. The above description is illustrated in Fig. 1. Energy resolution shows the ability of a detector to distinguish gamma-sources with slightly different energies, which is of great importance for gamma-spectroscopy.
     Emission spectrum is the relative number of photons emitted by scintillator as a function of wavelength. The Emission spectrum is shown in Fig. 2. The intensity maximum corresponds to the Imax wavelength shown in the table. For coefficient detection of emitted photons, the maximum of PMT quantum efficiency should coincide with Imax.
     Background is a quantity determined as a number of luminescent pulses emitted by radioactive substance within 1 second in the bulk of the scintillator with the weight of 1 kg.
     Most scintillation crystals reveal a number of luminescent components. The main component corresponds to Decay time, however less intense and slower ones also exist. Commonly, the strength of these components is estimated by using the intensity of a scintillator's glow, measured at specified time after the Decay time. Afterglow is the ratio of the intensity measured at this specified time (usually, after 6 ms) to the intensity of the main component measured at Decay time.

     Complex oxide crystals Gadolinium Silicate doped with Cerium (Gd2SiO5(Ce) or GSO), BGO, CWO and PWO have a number of advantages over alkali halide crystals: high effective atomic number, high density, good energy resolution in the energy region over 5 MeV, low afterglow, and non-hygroscopicity. Due to these features, detectors with oxide crystals are fail-safer, have no need of hermetization, and have mass and volume several times less than Alkali Halide analogues at the same detection efficiency. Yet oxide scintillators are characterized by lower light output and somewhat lower energy resolution at energies less than 5 MeV.
     Bismuth Germanate (Bi4Ge3012 or BGO) is one of the most widely used scintillation materials of the oxide type. It has high atomic number and density values. Detectors based on BGO have volume 10 - 4 times and mass 5 - 7 times less than those with Alkali Halide scintillators. BGO is mechanically strong enough, rugged, non-hygroscopic, and has no cleavage .BGO has an extreme high density of 7.13 g /cm3 and has a high Z value which makes these crystals very suitable for the detection of natural radioactivity (U, Th, K), for high energy physics applications (high photofraction) or in compact Compton suppression spectrometers.
BGO detectors are characterized by high energy resolution in the energy range 5 - 20 MeV, a relatively short decay time; its parameters remain stable up to the doses of 5 x 104 Gy; large-size single crystals are possible to obtain. Due to these features, BGO crystals are used in high-energy physics (scintillators for electromagnetic calorimeters and detecting assemblies of accelerators), spectrometry and radiometry of gamma-radiation, positron tomography
     Cadmium Tungstate (CdWO4 or CWO) has high density and atomic number values. Therefore, for CWO, the light output is 2.5 - 3 times higher than that of Bismuth Germanate. Due to low intrinsic background and afterglow and to rather high light output of CWO, the most suitable areas of its application are spectrometry and radiometry of radionuclides in extra-low activities. CWO is the most widely used scintillator for computer tomography. A rather great decay time value (3 - 5 Cls) is a significant feature of CWO which restricts the possibilities of its application in many cases.
     Lead Tungstate (PbWO4 or PWO) is a heavy (density = 8.28 g/cm3, Z = 73) and fast (decay time = 3 - 5 ns) scintillation material. It has the least radiation length and Moliere radius values (0.9 and 2.19, respectively) among all known scintillators. Radiation damage appears at doses exceeding 105 Gy. Yet the light output of PWO is as low as about 1% of Csl(TI), so that the material can be used in high-energy physics only.
     Double Natrium-Bismuth Tungstate (NaBi(WO4)2 or NBWO) is a new material that can be used as a Cherenkov radiator for particle detection. This crystal has scheelite structure of the space group C64h. Na+ and Bi3+ cations are statistically distributed among structural 4a positions (structural-statistic disorder). The unit cell contains two formula units. The unit cell parameters according to x-ray data are: a=5,281±0,001 Å; c=11,510±0,002 Å; the density r=7,588±0,004 g/cm3. Optical and luminescent properties of NBW are scarcely studied because this crystal can hardly be used as a scintillator due to low quantum yield of its luminescence. It was reported that X-ray luminescence spectrum has maximum ~520 nm and the luminescence intensity is about 5% of BGO intensity.
     Thallium doped Sodium Iodide NaI(Tl) is the most widely used scintillation material. NaI(TI) is used traditionally in nuclear medicine, environmental measurements, geophysics, medium-energy physics, etc. The fact of its great light output among scintillators, convenient emission range (in coincidence with maximum efficiency region of photomultiplier (PMT) with bialkali photocatodes), the possibility of large-size crystals production, and their low prices compared to other scintillation materials compensate to a great extent for the main Nal(TI) disadvantage. Which is namely the hygroscopicity, on account of which NaI(TI) can be used only in hermetically sealed assemblies. Varying of crystal growth conditions, dopant concentration, raw material quality, etc. makes it possible to improve specific parameters, e.g., to enhance the radiation resistance, to increase the transparency, and to reduce the afterglow. For specific applications, low-background crystals can be grown. NaI(TI) crystals with increased dopant concentration are used to manufacture X-ray detectors of high spectrometric quality. NaI(TI) is produced in two forms: single crystals and polycrystals. The optical and scintillating characteristics of the material are the same in both states. In some cases of application, however, the use of the polycrystalline material allows coping with a number of additional problems. First, a press forging makes it possible to obtain crystals with linear dimensions exceeding significantly than those of grown single crystals. Second, the polycrystals are ruggedized, which is important in some cases. Moreover, NaI(TI) polycrystals do not possess the perfect cleavage, so the probability of their destruction in the course of the use is reduced. The use of extrusion in converting NaI(TI) into the polycrystalline state makes it also possible to obtain complex-shaped parts without additional expensive machining.
     The most important feature of Cesium Iodide crystals doped with Thallium CsI(Tl) is their emission spectrum having the maximum at 550 nm, which allows photodiodes to be used to detect the emission. The use of a scintillator-photodiode pair makes it possible to diminish significantly the size of the detecting system (due to the use of photodiode instead of PMT), to do without high-voltage supply source, and to use detecting systems in magnetic fields. The high radiation resistance (up to 102 Gy) allows CsI(TI) to be used in nuclear, medium and high-energy physics. Special treatment ensures obtaining of CsI(TI) scintillators with a low afterglow (less than 0.1% after 5 ms) for the use in tomographic systems.
     Cesium Iodide doped with Sodium CsI(Na) is a widely used material nowadays. High light output (85% of that of NaI(TI)), emission in the blue spectral region (in coincidence with the maximum sensitivity range of the most popular PMT with bialkali photocatodes), and substantially lower hygroscopicity in comparison with that of NaI(TI) makes this material a good alternative for NaI(TI) in many standard applications. The temperature dependence of light output has its maximum at 80°C. This makes it possible to use CsI(Na) the scintillation material at elevated temperatures. The decay time of CsI(Na) depends on the dopant concentration and varies in the range of 500 - 700 ns.
     Zinc Selenide ZnSe(Te) scintillation material was created especially for matching with photodiode, which its emission maximum is at 640 nm. Matching coefficient between scintillator and photodiode is up to 0.9. ZnSe scintillators are sharply different from ZnS. "Fast" ZnSe has the time decay of 3 - 5 µs, "slow" - 30 - 50 µs. These are used preferably for X-rays and gamma-particle registration. Crystals ZnSe(Te) do not have very good transparency. Relative to CsI(Tl), light output for X-rays with E<100 keV (CsI(Tl)=100%) is up to 170% at 2 mm thickness. Non-uniformity is usually less than 1%. Crystals ZnSe(Te) are non-higroscopic and good enough for mechanical treatment without any cleavage. Standard ZnSe(Te) boules have a diameter of 24 mm. Diameters up to 40 mm are available on request.

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      Film technologies are becoming more and more important for the development of modern sciences and technologies. The development of film technology needs various and high quality single crystalline substrates. Firstly, the cell parameter of the substrate must match with the film to be grown on the substrate vary well, so that only special single crystal which has certain lattice constant, correct orientation and high fabrication accuracy can be used for the film. Secondly, the substrate crystal must be structure perfect, crystal structure defect such as twin and inclusion must be as few as possible. The surface of the substrate must be polished to very high flatness and micro roughness (the test result of AFM should be better than a few angstrom in an 5x5 µm area for example). The substrate must be able to stand to high, low temperature and chemical environment during the film growth and use process. Also some physical, mechanical properties are necessary for the substrate. For example, the microwave dielectric loss must be very low for the substrates used in microwave communication.
      Gadolinium Gallium Garnet (GGG, Gd3Ga5O12) is a magneto-optical and microwave substrate. It is the best substrate material for infrared optical isolator (1.3 and 1.5 µm), which is a very important device in optical communication. It is made of YIG or BIG film on the GGG substrate plus birefringence parts. Also GGG is an important substrate for microwave isolator and other devices, its physical, mechanical and chemical properties are all good for the above applications.
      Zinc Oxide (ZnO) can be grown as a single crystal semiconductor with very interesting properties. The bandgap is in the 3.4 eV range which makes it attractive for many of the blue and violet applications in opto-electronics as well as UV devices. It is available in bulk, in wafers up to 2 inches, which gives it a major advantage over Gallium Nitride and other group III Nitrides.
ZnO also has the potential to become the substrate material of choice for GaN. Like GaN it has a wurtzite structure, with lattice constants closely matched to GaN (a=3.249, c=5.205). ZnO is exactly lattice matched to InGaN with a 22% In content. Perhaps most importantly it is a soft compliant material that is believed may take up the lattice stress in preference to the growing GaN layer. It suffers from the drawback that it dissociates in ammonia at temperatures above 600°C. With its wide bandgap Zinc Oxide could prove very useful in optical applications as well as many high speed electronics. ZnO may also be used as a substrate for epitaxial growth.

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      Tellurium (Te) was discovered in 1783 by Baron Franz Josef Müller von Reichenstein in Sibiu, Roumania. Tellurium is a silvery-white, metallic-looking in bulk, but is usually obtained as a dark grey powder. It is a semi-metal. Tellurium burns in air or oxygen, is unaffected by water or HCl, but dissolves in HNO3. It is used in alloys to improve machinability, in electronics, and in catalysts.
      Tellurium has p-type semiconductor properties and, hence, is used in the electronics industry. Tellurium compounds (tellurides) are semiconducting materials and used for photoreceptors in solar cells. Te is also used in the refining of zinc where it eliminates cobalt from the process. Contact with either the pure metal or its compounds is to be avoided as they are not only toxic, but inhalation of the vapours leads to unpleasant body odours !

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      The effect of light diffraction by acoustic wave is wide used in the Acousto-Optic (AO) Devices. Typically, ultrasonic wave is generated with LiNbO3 piezotranducer bonded to AO crystal. The intensity, direction and wavelength of the diffracted light are related with power and frequency of RF signal applied to piezotransducer. The following AO devices can be produced: modulators, deflectors, AO tunable filters (AOTFs), laser Q-switches, RF spectrum analyzers.
     Laser quality Tellurium Dioxide (TeO2 or Paratellurite) is an excellent piezo-optical material. It is extensively used because of it's high acousto-optical figure of merit in making acousto-optical modulators, imaging devices, splitters, deflectors, tunable polarisation filters, radio frequency spectral analysers and other acousto-optoelectronic equipment for laser radiation control. TeO2 crystals are grown by Czochralsky method, it has higher damage threshold and better optical quality if compared with TeO2 crystals grown by some other methods.
     Lead Molybdate (PbMoO4 or PM) crystal is one of the most efficient materials used for acousto-optic devices. It has been extensively used for acousto-optic modulators, deflectors and phase-shifters. Crystals of Lead Molybdate with the diameter up to 60 mm and 60 - 80 mm length are grown by Czochralsky-Kyropulos method. Lead Molybdate AO elements possesses low optical losses, high optical homogeneity, stability to laser radiation. High crystal homogeneity also allows vacuum thermo - pressure bonding for large aperture devices.

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      Water-soluble Triglycine Sulfate crystals have technological importance for room-temperature infrared detectors, earth exploration, radiation monitoring and astronomical telescopes. TGS is the best material applied as a sensitive element in pyroelectric sensors due to its high pyroelectric coefficient, reasonably low dielectric constant, and the best quality factor. Pyroelectric sensors based on TGS are uniformly sensitive to radiation in wavelength range from ultraviolet to far infrared and do not require cryogen cooling for operation. Using of deuterated DTGS crystals allows to extend temperature range of sensing due to their higher Curie temperature.

            Triglycine Sulphate                         TGS       (NH2CH2COOH)3 H2SO4
            Deuterated Triglycine Sulphate       DTGS       (ND2CD2COOD)3 D2SO4
            L-α-Alanine Doped TGS                         ATGS       L-α-Ala (NH2CH2COOH)3 H2SO4
            L-α-Alanine Doped DTGS                        ADTGS       L-α-Ala (ND2CD2COOD)3 D2SO4

Doping with La -Alanine significantly improves and orders domain structure and turns the material to a hard ferroelectric.

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      Titanium doped Sapphire (Ti3+:Al2O3 or Ti:Sapphire) is the most widely used crystal for wavelengths tunable lasers. It combines the excellent thermal, physical and optical properties of Sapphire with the broadest tunable range of any known material. It can be lased over the entire band from 660 to 1100 nm. Frequency doubling provides tunability over the blue-green region of the visible spectrum.
     Ti:Sapphire crystals are active media for highly efficient tunable solid-state lasers. They demonstrate good operation in the pulsed-periodic, quasi-CW and CW modes of operation. Ti:Sapphire is a 4-level, Vibronic laser with fluorescence lifetime of 3.6 µm. The peak of the absorption band is 490 nm which makes it an excellent material for pumping with a variety of sources operating in the green-argon ion, copper vapour, frequency-doubled Nd:YAG, and dye lasers are routinely used. Crystals have also been flashlight pumped by lamps designed to allow short fluorescence lifetime. These factors and broad tunability make it an excellent replacement for several common dye lasing materials. The crystals are grown using Czochralsky and Ciropolous techniques.

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     Roentgenophosphors convert X-ray radiation into visible light with spectrum matched to spectral response of roentgenographic films. Roentgenophosphors provide the possibility to manufacture diverse intensifying screens for medical and industrial radiography (roentgenology, defectoscopy) and possibility of optimum choice with taking into account radiological safety of a patient.
     The described roentgenophosphors can be used within temperature range from -50°C to +85°C and relative humidity upto 80%.

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      Neodymium doped Yttrium Aluminum Garnet (Nd:Y3Al5O12 or Nd:YAG) crystal, which continues as the best of the rare earth garnet materials that are characterized by four-level laser operation which permits low threshold pulse and cw operation, is the most mature and widely used solid-state laser material adopted by R&D, medical, industrial and military customers. Its main and obvious advantages are: high gain, low threshold, high efficiency, low loss at 1.064 µm, as well as high optical quality, good thermal conductivity and thermal shock characteristics, stable chemical and mechanical properties, which make Nd:YAG as the most suitable and commercial laser material for various modes of operation (CW, pulsed, Q-switched, mode locked and cavity dumped).
      Erbium doped Yttrium Aluminum Garnet (Er:Y3Al5O12 or Er:YAG) combine various output wavelength with the superior thermal and optical properties of YAG. It is a well known material for medical applications.
      Ytterbium doped Yttrium Aluminum Garnet (Yb:Y3Al5O12 or Yb:YAG) is one of the most promising laser-active materials and more suitable for diode-pumping than the traditional Nd-doped crystals. It can be pumped at 0.94 µm and generates 1.03 µm laser output. Compared with the commonly used Nd:YAG crystal, Yb:YAG crystal has a larger absorption bandwidth in order to reduce thermal management requirements for diode lasers, a longer upper-state lifetime, three to four times lower thermal loading per unit pump power. Yb:YAG crystal is expected to replace Nd:YAG crystal for high power diode-pumped lasers and other potential applications, such as, its doubling wavelength is 515 nm very close to that of Ar-ion laser (514 nm), which makes it possible to replace large volume Ar-ion laser.

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      Undoped Yttrium Aluminium Garnet (Y3Al5O12 or YAG) is a new substrate and optical material that can be used for both UV and IR optics. It is particularly useful for high-temperature and high-energy applications. The mechanical and chemical stability of YAG is similar to that of Sapphire, but YAG is not birefringent. This particular feature is extremely important for some optical applications. We provide high quality and optical homogenity YAG with different dimensions and specifications for the use in industrial, medical and scientific fields.

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     Practically all Rare Earths ions may be injected into YLF lattice. Maximal possible concentration is different for different Rare Earths. For example Y may be 100% replaced with Yb or La, 50% - with Er, for Nd reachable concentration is to 1.5%.
     Pattern wavelengths are:
           Nd:YLF           1.047 µm, 1.053 µm, 1.313 µm, 1.324 µm and 1.370 µm
          Er:YLF           0.85 µm and 2.81 µm
          Ho:YLF           0.75 µm and 2.06 µm
          Tm:YLF           0.435 µm, 1.89 µm and 2.30 µm
     Nd:YLF (Nd:LiYF4) offers an alternative to the more common YAG host for near IR operation. The combination of weak thermal lensing (19 times lower than that of YAG), large fluorescence line width and naturally polarized oscillation makes Nd:YLF an excellent material for CW, modelocked operation. 1.053 µm output of Nd:YLF matches gain curves of Nd:Glass and performs well as an oscillator and pre-amplifier for this host. YLF is grown utilizing the modified Czochralsky technique. The as-grown crystals are then processed into laser rods or slabs, coated in house, and inspected per customer specifications. Long crystals for lamp pumping with concentration to 1.1 atom % and short elements for diode pumping with concentration to 1.5 atom % can be grown.
     The Er:YLF, Ho:YLF and Tm:YLF single crystal rods are designed to be applied in solid-state lasers which are widely used for industrial, medical and scientific applications. Pure YLF crystals are transparent within the spectrum band of 0.12 - 7.5 µm, photo-, thermo- and radiation-resistant. The YLF crystals have low values of non-linear refraction index and thermooptical constants.

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      Active elements from Erbium doped Yttrium Scandium Gallium Garnet crystals (Er:Y3Sc2Ga3012 or Er:YSGG) single crystals are desinged for diode pumped solid-state lasers radiating in the 3 µm range. Er:YSGG crystals show the perspectiveness of their application alongside with the widely used Er:YAG, Er:GGG and Er:YLF crystals.
      Flash lamp pumped solid-state lasers based on Cr,Nd and Cr,Er doped Yttrium Scandium Gallium Garnet crystals (Cr,Nd:Y3Sc2Ga3012 or Cr,Nd:YSGG and Cr,Er:Y3Sc2Ga3012 or Cr,Er:YSGG) have a higher efficiency than those based on Nd:YAG and Er:YAG. Active elements manufactured from YSGG crystals are optimum for medium power pulse lasers with the repetition rates up to several tens of cycles. The advantages of YSGG crystals compared with YAG crystals are lost when large size elements are used because of the worse thermal characteristics of YSGG crystals.

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      Nd doped Yttrium Vanadate (Nd3+:YVO4) is one of the most effective and advanced materials for diode pumped lasers. Compactly designed Nd3+:YVO4 lasers with green, red and blue light output are really perfect means for material processing, spectroscopy, medical diagnostics, laser printing and other applications. Compared to Nd3+:YAG and Nd3+:YLF, Nd3+:YVO4 diode pumped lasers have: wide absorption bandwidth, low lasing threshold, high slope efficiency, large luminescent cross-section, linearly polarized emission and single-mode output.
      Yttrium Vanadate doped with Er3+ or Yb3+ and also with a combination of Er3+, Yb3+ (YVO4:Er3+; YVO4:Yb3+; YVO4:Er3+,Yb3+) work on wavelenghts of 1.54, 1.61 µm and are used in eyesafe laser applications. In contrast to Er3+, Yb3+ doped phosphate glass, Er3+, Yb3+:YVO4 crystals can be used in CW mode with high pump energy and high efficiency. Its thermal conductivity is much higher than that of glass and this improves pump characteristics of the laser and relaxes cooling requirements. Yb3+:YVO4 has a wide absorption bandwidth at 0.98 µm and can generate with high effectivity at 1.02 µm due to low losses of the pump energy.
      Combined Yttrium Vanadate (YVO4 /Nd3+:YVO4) crystals combined during growth process are principially different from analoguous composite crystals, produced by bonding undoped and Nd3+ doped YVO4 crystals utilizing thermal diffusion. In case of thermal diffusion at the bonding interface optical losses can be examined, which lead to lower laser efficiency, and at certain laser conditions cracks can appear on this interfaces resulting in damage of the optical element. The combined crystals do not have such bonding interfaces and for this reason mentioned problems do not occur. The combined crystals have about 10-15% higher output generation characteristics and a higher damage threshold compared to composite crystals.
      New Nd3+-doped gadolinium vanadate crystals Nd3+:GdVO4 allow to create effective diode-pumped lasers for applications in medicine and technique.

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Literature:
    • F. Rotermund, V. Petrov, F. Noack and P. Schunemann. Characterization of ZnGeP2 for parametric generation with near-infrared femtosecond pumping. Fiber and Integrated Optics 20 (2001) 139-50
    • G.A.Verozubova, A.I.Gribenyukov, V.V.Korotkova, O.Semchinova, D.Uffmann. Synthesis and growth of ZnGeP2 crystals for nonlinear optical applications. Journal of Crystal Growth (2000) Vol 213, 3-4, 334-339
    • Madarasz, F. L., J. O. Dimmock, N. Deitz, and K. J. Bachmann, Sellmeier parameters for ZnGeP2 and GaP, J. Appl. Physics, 87, 1564-1565 (2000)
    • V. Petrov, F. Rotermund, F. Noack and P. Schunemann. Femtosecond parametric generation in ZnGeP2. Opt. Lett. 24 (1999) 414-6
    • V. Petrov, Y. Tanaka and T. Suzuki. Parametric generation of 1-ps between 5 and 11 µm with a ZnGeP2 crystal. IEEE J. Quantum Elect. QE-33 (1997) 1749-55
    • K. Stoll, J.-J. Zondy, O. Acef. Fourth-harmonic generationof a continuous-wave CO2 laser by use of an AgGaSe2/ZnGeP2 doubly resonant device. Optics Letters, 1997, Volume 22, Issue 17, 1302-1304
    • K. L. Vodopyanov. Parametric generation of tunable infrared radiation in ZnGeP2 and GaSe pumped at 3 µm. JOSA B, 1993, 10, 9, 1723

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      Chemically vapor deposited zinc selenide (CVD ZnSe) is the material of choice for use as optical components in high powered CO2 lasers due to its low bulk absorption at 10.6 microns. Its index of refraction homogeneity and uniformity offers excellent optical performance for use as protective windows or optical elements in high resolution forward looking infrared (FLIR) thermal imaging equipment. This material has also been used as small windows and lenses in medical and industrial applications, such as thermometry and spectroscopy. It has extremely low bulk losses due to absorption and scatter, has a high resistance to thermal shock and is stable in virtually all environments.
      Zinc selenide is a relatively soft material and scratches rather easily. It requires an antireflection coating due to its high refractive index if high transmission is required. ZnSe has a rather low dispersion across its useful transmission range. For high power applications, it is critical that the material bulk absorption and internal defect structure be carefully controlled, that minimum-damage polishing technology be employed, and the highest quality optical thin film coatings are used.

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