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The filamentation phenomenon arising at the intersection of two femtosecond laser beams in a sapphire single crystal has been studied. Conditions for a regular multifilament structure (MFS) to emerge with the parameters depending on the pulse energy, intersection angle, and phase difference between two exciting beams are determined. For the first time, the formation of a single filament under the action of two different excitation beams is analyzed as an MFS implementation. The number of filaments in the MFS is demonstrated to depend on the number of interference maxima in the intersection region of beams, the power of which exceeds the critical power of self-focusing. Attention is paid to the possibility to control the multifilament structure by varying the phase difference between the interacting beams. Optical manifestations of the interaction between the filaments with the “attractive” or “repulsive” character are observed. The spectrum of the axial emission by a single filament, as well as its dependence on the filament length, is studied, and the process of four-wave mixing is shown to play a key role in its formation., Дослiджено явище фiламентацiї при перетинi двох фемтосекундних лазерних променiв у монокристалiчному сапфiрi. Визначено умови утворення регулярної мультифiламентної структури (МФС), параметри якої залежать вiд енергiї iмпульсу, кута перетину i рiзницi фаз мiж двома збуджуючими променями. Вперше, як окрему реалiзацiю МФС, дослiджено процес формування одинарних фiламентiв при дiї двох рiзних променiв збудження. Продемонстровано, що число фiламентiв в МФС залежить вiд кiлькостi iнтерференцiйних максимумiв в областi перетину променiв, потужнiсть яких перевищує критичну потужнiсть самофокусування. Звернуто увагу на можливiсть керування мультифiламентною структурою шляхом змiни рiзницi фаз мiж взаємодiючими променями. Спостережено оптичнi прояви “притягувального” i “вiдштовхувального” характеру взаємодiї фiламентiв. Вивчено спектр осьового випромiнювання одинарного фiламента залежно вiд його довжини. Показано, що у формуваннi осьового спектра його випромiнювання визначальну роль вiдiграє процес чотирихвильового змiшування.

We report on the experimental observation of periodic modulation of the axial luminescence intensity along the femtosecond filament track in sapphire and crystal quartz. The physical reason for the modulation is a cyclic transformation of the polarization state of the light pulse traveling in birefringent medium, caused by the phase raid between the ordinary and extraordinary rays, and different cross sections of multiphoton absorption for linear and circular polarizations.

Hexagonal single crystals of the Cr2+:Zn1-xMgxSe solid solution are grown by the Bridgman – Stockbarger technique. We study their optical and photoluminescent characteristics and determine the temperature dependences of the photoluminescence kinetics within the range 5 – 440 K. The crystals possess a broad gain band in the range from 2 to 3.5 μm and exhibit a weak quenching of luminescence with a quantum yield exceeding 80% at room temperature. Tunable continuous-wave oscillation is demonstrated in the region of 2.5 μm.

Nanocomposite films containing nanocrystals of silicon and silicon carbide are fabricated by direct ion-beam deposition onto silicon substrates. The films obtained are by Raman spectroscopy and the photoluminescence method. It is found that the samples under study exhibit two photoluminescence bands, in the “red” and near-infrared (IR) (600–1000 nm) and “blue” (400–550 nm) spectral ranges, which are accounted for by, respectively, the radiative recombination of excitons in silicon nanocrystals and radiative transitions between levels related to local centers (defects) on the surface of silicon nanocrystals and in the surrounding matrix. Short-duration treatment of the films in a solution based on hydrofluoric acid leads to modification of the emission spectrum and to an increase in the intensity of the exciton band due to the passivation of defects on the surface of silicon nanocrystals.

Optical and nonlinear optical properties of a novel composite system based on KDP single crystals with embedded nanoparticles of nanostructured oxyhydroxide of aluminum (Al 2 O 3 · n H 2 O, NOA), were studied. KDP crystals with NOA nanoparticles (KDP:NOA) possess high optical quality and homogeneity. Optical spectroscopy showed the presence of an absorption band at 270 nm caused by NOA nanoparticles incorporated in the KDP matrix. There was observed an enhancement of nonlinear refractive index and inversion of its sign in KDP:NOA crystals in comparison with nominally pure KDP crystals under excitation of picosecond laser pulses. The obtained results demonstrate that KDP:NOA is a promising composite material for optoelectronics and nonlinear optics.

The present paper brie y overviews the application of the Czochralski method for growth of a set of oxide crystals for photonics, as well as the design of equipment at the Institute for Single Crystals, NAS of Ukraine. The examples of crystal growth and their characterization are described. The simultaneous Q-switched lasing and self-Raman frequency conversion were demonstrated in Nd-doped PbWO4 and PbMoO4 crystals grown by the Czochralski method. The slope lasing e ciency obtained for a PbMoO4:Nd 3+ laser is the best result for all the crystals with the scheelite-type structure. A detection unit with high scintillation characteristics based on a large volume (V ≈ 350 cm) CdWO4 crystal was produced. Crystal growth procedures and properties of new double tungstate and vanadate crystals are presented, too.

Studied are peculiarities of the changes in the structure and electrophysical properties of nanocrystalline silicon carbide films of 3C-SiC polytype subjected to the action of picosecond laser pulses with λ = 355 nm and a pulse power up to 1.5 W. It is established that laser processing of the films with an energy density of 3 × 10−2−30 J/cm2 leads to ablation without decomposition of SiC. During the laser processing the electrical resistance of the films rises due to diminution of the film thickness. While measuring the PL properties of nc-SiC films under the influence of the applied electric field with intensity 3 × 103 V/cm, the effect of a single triple enhancement of the luminescence maximum is revealed. Repeated PL measurements at the same area of the film under the applied electric field with the intensity ranging from 0 to 1 × 104 V/cm show that the PL emission intensity diminishes at the short-wavelength boundary of the maximum and rises at the long-wavelength boundary. Thereat the spectral position of the PL maximum remains unchanged.

The triple-crystal X-ray diffractometry of anomalous X-Ray transmission is used to investigate sapphire single crystals grown in protective gaseous media with the help of the horizontal directional-crystallization method. The dependences between the integral intensities of anomalously transmitted and Bragg-Laue reflected X-ray beams (Ti and Ri, respectively) and the thickness of the samples under study, which enable us to determine regions of thin- and thick-crystal approximation, have been obtained at 2.52 ≤ μt ≤ 18.9. The integral coefficient μi of interference absorption and the integral characteristic yi are calculated in the dynamic thick-crystal approximation. It is demonstrated that dislocations are distributed mainly within the small-angle boundaries of a grown sapphire crystal. It is ascertained that the parameter μi is highly sensitive to the dislocation density and the pattern of the dislocation distribution in a crystal.

The optical and photoluminescence (PL) properties of nanocrystalline 3C-SiC films and the effect of the boundary regions between the nanocrystals were studied for two sets of films: (a) films with 10–15 nm nanocrystal size obtained by direct ion deposition method and (b) similar films annealed in oxygen at 850–950 °C. It was shown that annealing of the nanocrystalline SiC films resulted in weaker absorption in a broad spectral range, and to the increase of the optical band gap from 1.8 to 2.2 eV. On the contrary, the edge PL bands in the UV range (2.2 to 2.4 eV) remained similar. In the IR range, three maxima absent in the as-grown films, appeared at 1.52 eV, 1.56 eV and 1.63 eV. Measurement of the intensity of PL maxima as a function of the excitation power showed a nonlinear dependence that was attributed to the onset of stimulated emission.

The characterization of new gain-switched Fe:Cr:Zn1-xMgxSe laser working at the room temperature and its comparison to Fe:ZnSe laser was performed. The laser oscillation behavior, generation efficiency and output wavelength tuning possibilities were demonstrated. It was shown that the absorption and luminescence spectra of Fe:Cr:ZnMgSe crystal are shifted towards longer wavelengths in comparison with Fe:ZnSe active material. The difference is approximately 300 nm and it corresponds to measured absorption and emission spectra. The maximal Fe:Cr:ZnMgSe laser generated energy and the slope efficiency with respect to the absorbed energy were 200 ?J and 4.5%, respectively.

The impact of titanium dioxide (anatase) nanocrystals on growth process, optical and structural properties of KDP single crystal was studied. As-grown crystals were characterized by High Resolution Three-crystal X-ray Diffractometer, optical diagnostics of elastic scattering, cone-shaped interference method, and spatial profile analysis method. In the composite system KDP:TiO2 the effect of giant nonlinear optical response of anatase nanoparticles was revealed, in particular in the intensity range up to 20 MW/cm2 the change of sign of the nonlinear refraction index was found. These results can be explained by the resonance excitation of defective states on TiO2 nanoparticle surface.

A laboratory setup for direct ion deposition intended for obtaining silicon carbide films under the conditions of the condensation of carbon and silicon ions with energies of ≥100 eV is described. The setup contains an original vacuum-arc source of carbon-silicon plasma with an extended cathode and an inhomogeneous magnetic field. The design features of the plasma source, the main technological characteristics of the setup, and the regimes of deposition of nanocrystalline silicon carbide films are presented.

The study demonstrates the possibility of forming heterostructures consisting of nanocrystalline SiC layers of the cubic 3C polytype (the lower layer on the substrate) and the rhombohedral 21R polytype (the upper layer) by direction deposition of nanocrystalline SiC layers onto a substrate subjected to gradient heating. The structure and order of arrangement of the SiC layers are analyzed in detail by X-ray diffraction studies, femtosecond photoluminescence measurements, and optical spectroscopy. The nature of the peaks observed in the photoluminescence, optical reflectance, and absorption spectra is discussed.

The laser properties of Bridgman method grown active crystals Cr2+:ZnMgSe and Fe2+:ZnSe were investigated at room temperature from the point of view of laser parameters. Cr2+:ZnMgSe crystal was pumped by the 1.66 μm wavelength radiation of pulsed Er3+:YAP laser. The maximum reached energy and slope efficiency with respect to absorbed pump energy was 4 mJ and 15%, respectively. The Cr2+:ZnMgSe laser oscillation spectrum was about 90 nm wide and centered at 2.47 μm. With the CaF2 prism placed inside the laser resonator the tuning within 2.3 – 2.6 μm range was demonstrated. The pumping of Fe2+:ZnSe crystal was made by Q-switched Er:YAG laser radiation with the wavelength 2.94 μm. The measured maximum output Fe2+:ZnSe laser energy was 0.58 mJ with the generated wavelengths 4.3 – 4.6 μm and with a slope efficiency in respect to absorbed energy of 38%. The study demonstrates quite promising perspectives of the Bridgman-technique-grown Cr2+:ZnMgSe and Fe2+:ZnSe crystals for development of the efficient at room-temperature working mid-IR tunable laser sources.

The effect of irradiation with electrons on the optical and electrical properties of the nanocrystalline rhombohedral 21R-SiC and 27R-SiC films is studied. The cycles of irradiation of nanocrystalline SiC films on sapphire substrates with electrons with the energy 10 MeV are conducted in the range of fluences from 5 × 1014 to 9 × 1019 cm−2. It is established that, at the irradiation doses above 1019 cm−2, the optical absorption of the films at the photon energies E > Eg becomes less efficient than the optical absorption of unirradiated films. It is established that the Urbach energy as a function of the irradiation dose exhibits a minimum at the dose ∼1017 cm−2 for the 21R-SiC films and ∼5 × 1017 cm−2 for the 27R-SiC films, suggesting that radiation induces some ordering in the films. As the dose is increased from 5 × 1017 up to 9 × 1019 cm−2, an increase in the Urbach energy and a decrease in the optical band gap are observed. The effect is attributed to an increase in the concentration of radiation defects in the films.

Potassium dihydrogen phosphate crystals (KDP, KH 2 PO 4 ) doped with the organic xylenol orange (XO) dye are grown, the XO concentration in the crystal matrix is about 10 ppm. The spectral and luminescent properties of nominally pure, dye-doped and dye-doped/annealed at 150 °C crystals (KDP, KDP:XO and KDP:XO an ) were measured. The annealing temperature effect on the degree of dye protonation in the crystal matrix is established. Analysis of the IR-absorption spectra reveals a strong interaction between the incorporated dye molecules and the hydrogen subsystem of the matrix. The nonlinear optical (NLO) properties of KDP, KDP:XO and KDP:XO an crystals are studied within the self-action effect of picosecond laser pulses at 532 nm. The mechanism of photoinduced bleaching and the effects of laser beam self-focusing (in KDP) and self-defocusing (in KDP:XO and KDP:XO an ) are supposed to be due to resonance excitation of the subsystems of intrinsic defects and dye molecules, correspondingly. For KDP:XO an it is shown that thermal annealing of intrinsic crystal defects leads to domination of more effective NLO response of the subsystem of dye molecules that is correlated with photoluminescence data.

This paper reports on the results obtained during the development of the technological process of growth of sapphire crystals for optoelectronics through horizontal directional crystallization in a gaseous argon medium at a pressure of 800 mmHg. The sapphire crystals intended for the use in optoelectronics have been grown from purified molten alumina according to the authors’ technology. It has been demonstrated that, under conditions of a high temperature gradient across the crystallization front and at a low content of reducing components (H2, CO) in the growth medium, it is possible to grow sapphire crystals satisfying the requirements of optoelectronics.

Spectral dependences of effective values of the real and imaginary parts of the low-frequency permittivity of the Cd1−xZnxTe crystals (x=0.12–0.16) with the Schottky barrier fabricated on the surface are measured. It is found that the boundary wavelengths of the characteristic portions of the measured dependences represented in the complex plane correspond to energies of photons, which cause the radical variations in the state of negatively charged and electrically neutral localized acceptor states. The variations in the energy spectrum of the localized states, which are determined by the magnitude and polarity of the electric bias applied to the Shottky barrier, are found.

Compact broadly tunable Cr:ZnSe laser was constructed and described. Cr:ZnSe bulk crystal was grown by the Bridgman technique. In our best knowledge the bulk Cr:ZnSe prism was utilized as laser active media and simultaneously as an intra-cavity dispersive element for the first time. The maximal output pulse energy was 20 mJ. The generated radiation was tunable from 2000 up to 2750 nm. The repetition-rate was 1 Hz. The generated radiation beam spatial structure was close to TEM00.

The aim of the presented work was to design and characterize bulk Fe:ZnSe and Fe:Zn(1-x)Mg(x)Se (Mg content x = 0.19) lasers coherently pumped by electro-optically Q-switched Er:YSGG laser. This laser generated pumping radiation at 2.79 μm with the maximum energy of 50 mJ in 80 ns long pulse with the repetition-rate of 1 Hz. The 25 mm long optical resonator of Fe:ZnSe or Fe:ZnMgSe lasers was formed by a plan dichroic pumping mirror and a concave output coupler (r = 200 mm) with reflectivity 88 % @ 4-5 μm. Both lasers were operated at room temperature. Measured maximum output energy/slope efficiency in respect to the absorbed energy was ~ 3.8 mJ/42 % for the Fe:ZnSe laser and ~ 0.48 mJ/10 % for the Fe:ZnMgSe laser. The generated output pulse duration was 150 – 200 ns in both cases and the output beam spatial profile was approximately gaussian. The Fe:ZnSe and Fe:ZnMgSe lasers output spectra line-width was ~ 200 nm (FWHM) and their maxima were centered at 4.45 μm and 4.8 μm, respectively. The results were compared to pumping the same crystals by a Q-switched Er:YAG laser in similar conditions.

We synthesized a series of sol–gel silica matrices doped with laser dyes DCM, LK678, LD1, and LD2 which alcohol solutions have efficient lasing in the red spectral region and Rh800–in the near infrared (NIR) one. Absorption, fluorescence, and laser properties of the dyes in silica samples prepared by sol–gel process were investigated. It has found some peculiarities in preparation process of the laser matrices and in spectral characteristics of the dyes in these matrices.

Uniformity of properties of a semiconductor material is one of the important conditions to achieve high spectrometric performance of ionizing radiation detectors. To study uniformity of electrophysical properties of crystals, an original method for acquisition of distributions of local values of a dielectric permittivity /spl epsiv/' and tangent of a dielectric loss angle tan/spl delta//sub M/ in high-resistance semiconductors is offered. The method was approved on Cd/sub 1-x/Zn/sub x/Te (x=0.1 to 0.16) crystals grown by Bridgman method under high pressure of inert gas. Locality and reproducibility of measurements are provided by a special design of a movable electrode, with both the area and the hold-down pressure of the electric contact being unvaried. Differences in /spl epsiv/' and tan/spl delta//sub M/ distributions over the sample's area and an effect of uniform monochromatic illumination at a varied wavelength on these distributions are revealed. The physical nature of revealed irregularities is analyzed with involving results of researching CdZnTe crystals by diverse methods.

Projection microprocessing of materials by Nd: KGW laser shots (1.06 μm) is considered. Specifically, a practically feasible method of processing transparent materials (sapphire, fused quartz, and glass) by means of a laser-induced plasma is suggested. These materials are marked, in particular, by applying a controllable liquid-crystal mask on them. Also, a relief diffraction grating of period 3 μm is patterned on their surface. The effect of the transverse size of the area illuminated on the processing parameters is studied. It is established that the density and temperature of the laser-induced plasma grow with increasing transverse size of the torch, with the energy density of the laser radiation being the same. The plasma torch reverses the pressure and wavelength dependences of the rate of ablation of transparent materials as compared to those of metals.

Temperature dependence of spectroscopic characteristics as well as laser properties of the bulk Bridgman-grown Fe:ZnSe and Fe,Cr:Zn1-xMgxSe (x = 0.19, 0.38) active media were investigated under room and various cryogenic – liquid nitrogen - temperature . The pumping was provided by Er:YAG laser radiation at the wavelength of 2.94 μm, with energy 15 mJ in 110 ns Q-switched pulse or 200 mJ in 220 μs free-running pulse. The 55 mm long hemispherical resonator was formed by a dichroic pumping mirror (T = 92 % @ 2.94 μm and R = 100% @ 4.5 μm) and a concave output coupler (R = 95 % @ 4.5 μm, r = 200 mm). A strong dependence of generated output radiation parameters on temperature was observed for all samples.

YAG:Ce crystals have been grown by a new gas-phase horizontal directional crystallization (HDC) technique in a protective atmosphere and their cathodoluminescence (CL) spectra and scintillation characteristics have been studied. Using this HDC technology, it is possible to obtain large (110 × 150 × 35 mm) crystals with a high specific light yield (15 000–18 000 Ph/MeV) and good amplitude resolution (8–10%) for the excitation with 5.15-MeV α particles from a 239Pu source. In addition to an intense band at 550 nm due to Ce3+ ions, the CL spectra of crystals display an intrinsic emission band of YAG in the UV spectral range, which is due to the presence of YAl antisite defects.

It is shown that the developed method of solvent re-circulation, which provides optimum growth conditions at a constant temperature (Tcr = 80 °C, Vgrowth ∼ (0.8–1.6) × 10−6 cm/s, pH = 4), allows to grow KDP crystals with a cross-section up to 300 × 300 mm and a bulk laser damage threshold of ∼60 J/cm2.

The goal of this work was to design and investigate a Fe:ZnSe laser operating at room and cryogenic (down to liquid nitrogen) temperature. Pumping was provided by a Q-switched Er:YAG laser at the wavelength of 2.94 μm, the output energy 15 mJ, pulse duration 120 ns, and the repetition rate 1 Hz. Q-switched operation was achieved by the Brewster angle cut LiNbO3 Pockels cell placed between the rear mirror and the Er:YAG laser active medium. The pump radiation was directed into the Fe:ZnSe crystal placed in the vacuum chamber cooled by liquid nitrogen. The resonator was formed by a dichroic pumping mirror (T = 78 % at 2.94 μm and R = 100 % at 4.5 μm), and a concave output coupler (R = 95 % at 4.5 μm, r = 500 mm). Fluorescence spectra and lifetime of the bulk Bridgman-grown Fe:ZnSe crystal in the range from room temperature down to liquid nitrogen temperature were measured as well as the output characteristics of the Fe:ZnSe laser. The shift of the generated spectral line maximum of ~ 400 nm towards the shorter wavelengths was found for the change of temperature from room to the liquid nitrogen. Also the increase of lifetime was measured from 300 ns at the room temperature up to 100 μs at the temperature of 130 K. Maximum of generated output radiation at 130 K was 150 μJ with the central emission wavelength of 4.1 μm. At the room temperature the central emission wavelength of 4.45 μm was measured with the spectral line-width of ~100 nm. The generated output energy was 1.3 mJ. The comparison of results obtained for Fe:ZnSe active material with the new bulk Fe,Cr:ZnMgSe crystal was also made. The results obtained for Fe:ZnSe active material were compared with the investigation of new bulk crystal Fe,Cr:ZnMgSe.

The goal of this work was to design and investigate the gain switched new Fe,Cr:ZnMgSe laser operating at the room temperature. The pumping was provided by the electro-optically Q-switched Er:YAG laser with the oscillation wavelength of 2.937 μm which matching the absorption line of the Fe,Cr:ZnMgSe crystal. The Q-switched operation was obtained by the Brewster angle cut LiNbO 3 Pockels cell placed between the rear mirror and the laser active medium. The output radiation parameters were: the energy of 10 mJ, pulse duration of 120 ns, and repetition rate 1 Hz. The pump radiation was directed into the Fe,Cr:ZnMgSe crystal placed inside the 16 mm long hemi-spherical cavity formed by the dichroic pumping mirror (T = 86 % at 2.94 μm and R = 100% for 4 - 5 μm) and the output coupler with the reflectance R = 95 % at 4 - 5 μm and radius of curvature r = 500 mm. The maximum output Fe,Cr:ZnMgSe laser energy was 160 μJ corresponding the slope efficiency 4 % (with respect to absorbed energy). The generated radiation wavelength was 4.8 μm with the linewidth of 100 nm (FWHM). The output beam spatial profile was approximately Gaussian in both axes. Laser tuning properties were investigated by the Lyot filter (MgF 2 plate, 2 mm thick) inserted into the resonator providing the tuning range from 4.5 to 4.9 μm. The results were compared with the Fe:ZnSe crystal operated at the same conditions.

Summary form only given. Silicon carbide nanocrystal films have been synthesized by new original technique of direct ion deposition. Composition and structure of bonds between carbon and silicon atoms have been studied by means of photo-electron spectroscopy using XPS-800 Kratos spectrometer with MgK radiation. The spectra have been calibrated using data obtained for bond energies for reference SiC samples. The obtained films crystal structure has been studied by means of X-ray diffraction (DRON-2.0, CuK). The mean size of SiC nanocrystals was about 6-7 nm by Sherer formula estimation. The nonlinear refraction in nanocrystalline films of SiC has been studied by means of contemporary techniques. As a source of irradiation we used frequency doubled pulsed YAG:Nd laser. Experimentally have been shown that the nanocrystal films of SiC exhibit very high optical nonlinear response. Possible mechanisms of optical nonlinearity are discussed especially ones connected with the contribution of conducting electrons.

Cr:ZnSe laser active material is one of the favourite possibility how to generate broadly tunable mid-infrared laser radiation at room-temperature. The aim of this study was to demonstrate and analyze pulsed as well as continuous-wave laser action in bulk Cr:ZnSe crystals grown by the floating-zone method or by the Bridgman method. The absorption spectra of Cr:ZnSe were measured to be from 1500 to 2000 nm, therefore various lasers were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser (generated wavelength 1658 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm), and diodepumped Tm:YAP laser (generated wavelength 1980 nm). In the first case, the Cr:ZnSe crystal grown by the Bridgman method was investigated. In the second case, the Cr:ZnSe crystal grown by the floating zone method was studied. In both cases, the homogeneity of the active Cr:ZnSe crystals was found reasonable good. The emission spectrum was from 2000 up to 2800 nm. The Cr:ZnSe laser generated radiation was broadly continuously tunable in the range from 2050 nm up to 2750 nm. The generated radiation beam spatial structure was close to TEM 00 .

Broadly tunable mid-infrared laser sources operated at room-temperature are desired in many technological and medical applications. The aim of the project was to design and construct broadly tunable powerful Cr:ZnSe laser. The investigated Cr:ZnSe various shaped bulk crystals were grown by the Bridgman method or by the floating zone method. The absorption spectrum was measured to be from 1500 to 2000 nm and the emission spectrum was from 2100 to 2800 nm. Three different lasers were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser (generated wavelength 1660 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm) and diode-pumped Tm:YAP laser (generated wavelength 1980 nm). The constructed Cr:ZnSe laser operated in pulsed as well as in continuous-wave regime. In the first case the Cr:ZnSe crystal grown by the floating zone method was studied. The maximal output power in continuous-wave regime was 310 mW with the slope-efficiency 73% for the Tm:YAP laser pumping. In the second case the Cr:ZnSe prism grown by the Bridgman method which served simultaneously as laser active medium and intracavity dispersive element was investigated. For the Er:YAP laser pumping the maximal output energy was 20 mJ with the slope-efficiency 36%. The output radiation was tunable in the range from 2050 nm up to 2750 nm. For the Tm:YAP laser pumping the maximal output power in continuous-wave regime was 175 mW with the slope-efficiency 24%. The output radiation was tunable in the interval from 2220 nm up to 2680 nm. The generated radiation beam spatial structure was close to TEM00.

Cr:ZnSe crystals grown by the Bridgeman technique from the melt in inert gas (argon) under pressure were characterized and utilized as effective laser active material. Large crystalline boules with a necessary concentration of Cr 2+ ions 10 19 cm -3 , practically homogeneously distributed throughout the crystal bulk (50 mm in diameter and up to 100 mm in length), were prepared. For the laser evaluation the Cr:ZnSe samples in the form of 6 mm thick blocks were polished. Cr:ZnSe laser was longitudinally coherently pumped either with flashlamp-pumped Er:YAP laser radiation (emission wavelength 1658 nm) or with diode-pumped Tm:YAP laser radiation (emission wavelength 1980 nm). In the first case, the Cr:ZnSe laser was pumped with radiation of Er:YAP laser working in free-running regime (pulse length 200 ms, pulse energy 200 mJ, repetition rate 1 Hz). The maximal obtained Cr:ZnSe laser pulse energy was 14 mJ (slope-efficiency 73%). Using the dispersive prism inside the resonator, the output laser radiation was broadly tunable from 2150 nm up to 2600 nm. In the second case, the Cr:ZnSe laser was pumped with radiation of diode-pumped solid-state Tm:YAP laser working in pulsed as well as continuous-wave regime, for which the maximal obtained Cr:ZnSe laser output power was 200 mW (slope-efficiency 67%). The output spectrum of generated radiation covered the range from 2100 nm to 2400 nm. The temporal profile and spatial structure of laser beam were measured. The Cr:ZnSe crystal grown by the Bridgeman method was demonstrated as an efficient broadly tunable laser active material generated radiation in the mid-infrared spectrum and operated in room-temperature.

Different regimes of laser operation and stimulated Raman scattering (SRS) for a laser diode (LD)-pumped PbMoO4:Nd3+ crystal have been investigated. Under 1.5 W LD pumping, the output power of the PbMoO4:Nd3+ laser in the free-running mode at 1056 nm reached 0.65 W with a slope efficiency of up to 53%. Using different LiF: F-2 saturable absorbers, we achieved a maximum pulse energy of 11 microJ at a 1.4 ns pulse duration and a maximum output power of 0.35 W (10 microJ) at a 7 ns pulse width in the passively Q-switched mode. PbMoO4:Nd3+ self-Raman-laser operation at 1163 nm (first Stokes) was obtained for the first time, to our knowledge. The self-Raman-laser output pulse energy was measured to be as high as 6 microJ and the pulse duration was estimated to be shorter than 500 ps.

Knowledge of the spatial orientation of a dye in crystals is useful for investigation of the mechanisms of dye incorporation into a crystal and for creation of dye solid state lasers. It can be obtained by establishing anisotropy of the crystals' optical properties using polarization optical spectroscopy and luminescence methods. The aim of this work is to investigate the effect of xylenol orange dye incorporation into KDP crystals on anisotropy of their optical absorption and luminescence. The changes in the emission spectra and polarization of the emitted light are investigated for the case when the polarization plane of the exciting light is rotated about x, y, z crystal axes. It is observed that dichroic behavior of the transmission coefficient in different growth sectors of the crystals is different. The orientation of the transition dipole moment of the dye molecule is found for each growth sector.

The paper discusses about the electric properties of high-resistance CdZnTe crystals. The suggested method detects large-scale irregularities of various origins in high-resistance semiconductors. Grain boundaries and high-conductivity regions are easily revealed in Cd/sub 1-x/Zn/sub x/Te crystals. It was found that certain electric irregularities invisible by transmitted IR light are attributed to intrinsic structural defects.

We discuss a method of scanning photodielectric spectroscopy of crystals which is based on the measurements of small increments of the real /spl Delta//spl epsi/' and imaginary /spl Delta//spl epsi/" parts of dielectric permittivity, which are induced by a smooth variation of the photoexcitation wavelength. The spectral dependences of both parts of the dielectric constant upon the light wavelength were presented in the complex plane. Application of this method on Cd/sub 0.9/Zn/sub 0.1/Te crystals showed a possibility of determining the energy position of the localized states generated in the forbidden zone by the intrinsic structure defects.

The results of investigation of thermally stimulated and photoluminescence as well as absorption spectra of a-sapphire grown by a technique of horizontally directed crystallization in a protective gas medium of varying composition and pressure are presented. This technique has an advantage of minimization of W and Mo erosion, thus providing a considerably reduced prime cost. At the same time, there are some problems connected with emergence of considerable number of anion vacancies, whose in-axis concentration gradient is directed oppositely to that of dopants (mainly Ti). The correlations are found between the conditions of -sapphire growing and the data of absorption and luminescent spectroscopy. An interaction between the anion vacancies and Ti dopants, which induces a transition from electric-charge state Ti⁴+ to Ti³+, is discussed.

The effect of different crystallization parameters on optical absorption and laser damage threshold of KDP crystals was studied in the present paper. Crystals were grown in the direction of the prespecified angle of synchronism. A significant influence of the solution acidity, supersaturation value, hydrodynamic growth regime on the absorption spectra and bulk laser damage threshold of crystal was established. It was shown that crystals grown at pH equals 2,4 had an impurity - striated structure, the latter resulting in the decrease of bulk laser damage threshold and optical transparency of crystals. An essential improvement of optical transparency and increase of bulk laser damage threshold in crystals grown at pH equals 5 was found. For the first time established was the actually reached level of laser radiation resistance of rapidly grown oriented KDP crystals, grown at a rate of 5-10 mm/day. The obtained mean value of optical break through threshold is about 3 GW/cm 2 . This value is comparable with that typical for KDP crystals grown by a conventional method at a rate of 1 mm/day.

Photoinduced optical absorption and linear birefringence have been found in the garnet NaCa2Mn2V3O12 under illumination by He-Ne laser (λ = 633 nm). The effects are observed in the temperature range T < 130 K, persist a long time at low temperatures and reach the values ∆K ≈ 25cm−1 and ∆n ≈ 1.6•10−4.

The paper is devoted to studying the influence of Cu, Si, Pb and Cr impurities (possessing no absorption bands at the wavelength of acting laser irradiation) on the value of bulk laser damage threshold and UV absorption in KDP single crystals. It is shown that for the investigated concentration range (1(DOT)10 -5 - 1(DOT)10 -2 mass%) laser damage threshold essentially decreases with raising the concentration of impurity ions in the crystal lattice. The maximal value of the said characteristic (approximately 40 J/cm 2 ) is found to be achieved in the case when the concentration of impurities is not less than 1(DOT)10 -5 mass%.

The faulty microstructure of KDP samples having different bulk laser damage threshold (4 multiplied by 1010 W/cm2 - 5.4 multiplied by 1011 W/cm2 was studied using the methods of the three-crystal x-ray diffraction and two-crystal topography on reflection. A correlation between the dispersion of the structure-sensitive parameters characterizing the microfaultness and the value of bulk laser threshold of samples cut off large KDP crystals was established.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The results of the study of bulk laser damage threshold and structural characteristics of rapidly grown KDP crystals are presented in this paper. Crystals were grown in the direction of preset angle of synchronism at a rate of 10 mm/day. The developed technique allows to obtain blanks of nonlinear elements right during crystal growth thus decreasing material and power consumption when making products. The grown crystals have bulk laser damage threshold on the level of approximately 5 X 10 10 W/cm 2 and high structural quality.

The second harmonic generation efficiency was studied for the single crystalline potassium dihydrogen phosphate matrix with incorporated TiO2 nanocrystals in the field of the mode-locked Nd:YAG laser pulses. For the first time the frequency conversion efficiency gain was observed for KDP:TiO2 single crystal (SC) instead of KDP SC due to the internal self-focusing effect of the pump beam caused by the giant cubic nonlinear optical response of the embedded nanoparticles.

We observe temporal self-compression of the axial component of femto- second laser pulse in the filamentation regime in fused silica and find optimized conditions for the maximum compression. Using spatial filtration, we extract the ax- ial component of the pulse compressed down to the duration of 63 fs from the initial 160 fs one. The compressed pulse can be used as a probe in pump-probe measure- ments to improve their temporal resolution.

The optical and electro-optical properties of large-sized (diameter, 20 mm; length, 70 mm) single crystals of Zn1 − xMgxSe (x ∼ 0.5) semiconductor solid solutions are investigated. The crystals are grown by the vertical Bridgman-Stockbarger method. It is found that, for ZnMgSe single crystals with a magnesium content up to 25 at. %, the modulus of the difference between the electro-optical coefficients |r13 − r33| at a wavelength of 0.63 μm is equal to (1.1 ± 0.22) × 10−12 m/V, which is comparable in order of magnitude to the difference in the electro-optical coefficients for classical hexagonal AIIBVI compounds, such as CdS and CdSe. It is shown that single crystals of ZnMgSe solid solutions are promising materials for use in the fabrication of electro-optical modulators, λ/4-and λ/2-wavelength plates, and multifunctional optical elements operating in the range of high-intensity radiation of CO and CO2 lasers.

This paper is devoted to studying the influence of Ca, Si, Pb, and Cr impurities (possessing no absorption bands at the wavelength of acting laser irradiation) on the value of bulk laser damage threshold and UV absorption in KDP single crystals. It is shown that for the investigated concentration range (1 divided by 10-5 1 divided by 10-2 mass% laser damage threshold essentially decreases with raising the concentration of impurity ions in the crystal lattice. The maximal value of the said characteristic (approximately 40 J/cm2) is found to be achieved in the case when the concentration of impurities is not less than 1 divided by 10-5 mass%.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Investigated is the influence of isotermal annealing on the real structure and laser damage threshold of KDP single crystals. It is shown that the annealing of the samples at temperatures close to that of phase transition results in a pronounced decrease of the number of defects in the crystals,their optical homogeneity being improved. The chosen optical annealing conditions allow to raisethe values of mechanical strength and laser damage threshold by 2 or 3 times and thereby to reducethe spread of these characteristics over the bulk of the crystals. 1. INTRODUCTION The problem of the laser damage threshold of KDP crystals and the development of technological measures for raising this characteristic is especially topical at present in connectionwith the use of the said crystals as elements of high power laser systems. The typical value ofbulk laser damage of as - grownKDP crystals is 23 GW/cm2 (A=1 .06 4ti,r=1O nsec) or 68 J/cm2. Proposed in this research is a method for increasing the value of laser damage threshold of

In the present paper an attempt was made to grow crystals with high laser damage threshold. To choose the crystallization conditions, a study was carried out on the correlation between the crystallization conditions, real crystalline structure, absorption coefficient, and the value of the laser damage threshold.

The temperature and magnetic field dependences of the electric resistance of ceramic samples Ho0.55Sr0.45CoO3−δ and Ho0.45Sr0.55CoO3−δ at temperatures ranging from room to liquid-nitrogen temperature and magnetic fields to 7kOe, applied perpendicular to the direction of current transport, are studied. Electric conduction in these samples is of the semiconductor type, and the magnetoresistance in a narrow temperature interval and comparable fields changed sign, ranging from −50 to +120%. A nonlinear dependence of the resistance of the samples on the magnitude of the transport current for weak currents and high sensitivity of the resistance to a weak magnetic field are observed. Analysis of the data shows a magnetic contribution (the presence of low-spin (S=1) states t2g5eg1 or high-spin (S=2) states t2g4eg2 of the Co3+ ions) to the mechanism of interelectronic correlations under conditions of percolation conductivity of the systems investigated. The corresponding activation energies are estimated.

Three-dimensional mass transfer is simulated. The factors determining the hydrodynamic conditions for efficient mass transfer in growth of large KDP single crystals (cross sections up to 45 × 45 cm2) from solutions in a real 300-l-crystallizer are established. The conditions for the motion of the supersaturated solution to the surface of a growing crystal in the direction opposite to that of gravitation are attained. The growth mode developed provides growth rates that are five times higher of large high-quality optical KDP crystals.