Oxide single crystals, such as yttrium aluminum garnet (YAG) and yttrium orthovanadate (YVO₄), are important host crystals for solid-state laser applications. These crystals are often grown by the Czochralski process and are doped with neodymium during growth. The microstructure of the resultant crystal affects the overall laser performance and it is necessary to be able to characterize grown-in defects in the material. Scanning electron microscopy has been used to examine the fracture surfaces of YAG and has shown the presence of microscopic voids, which act as stress concentrators and in some cases appear to be the cause of fracture. Transmission electron microscopy (TEM) has been used to characterize various defects in both YAG and YVO₄ crystals. The defects found depend on the growth conditions, specifically the Nd concentration in the crystal and the position within the boule. One of the most common defects identified in both materials were microscopic spherical particles. In YAG these particles appeared to be located primarily in the core regions and analysis of high resolution images indicate that they are due to regions that are both compositionally and orientationally different from the matrix phase. Direct observation of dislocations in YVO₄ was made using TEM. In YAG only indirect evidence for dislocations could be found from the observation of river marks on fracture surfaces.

Investigations of thermal effects caused by absorption of laser radiation in Faraday isolators and Faraday mirrors are becoming more important. A most promising medium for Faraday devices in the wavelength range of 600-1200 nm is the terbium gallium garnet (TGG) crystal. In order to measure its thermo-optic constants (which are unknown) we used a scanning Hartmann sensor technique. This technique can easily and inexpensively measure wavefront distortions induced by optical elements to within 2nm.

Cerium has been doped in both LiCAF and LiSAF. However, each host has some intrinsic problems resulting in scatter and thermal expansion coefficient issues, respectively. In order to optimize the laser host, crystals were grown on various compositions of Ce,Na:LiSr_xCa_1-xAlF₆. The materials produced were characterized using a variety of methods, including differential thermal analysis, glow-discharge mass spectrometery, electron microprobe, and various microscopic techniques. Samples were fabricated to characterize the absorption and emission properties for each crystal composition. Finally, laser threshold and efficiency were characterized for the various samples. Through an analysis and comparison of these critical aspects, an optimized, commercially-viable crystal can be identified to be incorporated into a tunable, solid-state UV laser system. In the case of the selected crystal system, the crystal growth characteristics of the various crystals are very similar. In the case of the selected crystal system, the crystal growth characteristics of the various crystals are very similar. Absorption and emission values for the strontium-rich compositions are greater than those for the calcium-rich compositions. Lasing was achieved in all of the samples with different output coupler transmissions. The Sr/Ca=35/65 composition showed the highest output powers. Taking into consideration all three aspects of this resaerch, there exists an intermediate composition close to Sr/Ca=35/65, that would be an optimized host as a novel UV laser host.

Self passively Q-switching of a diode-pumped Cr,Nd:YAG, where the Cr⁴⁺ is used as a saturable absorber for the 1064 nm laser emission is reported. The maximum average output power was obtained using an output coupler of R=86%. The self Q-switched diode pumped laser yielded 1.86-W average output power with low threshold pumping power (≈1.7-W), average slope efficiency of ≈34%, pulse duration of about 14-16 nsec, and modulation frequency ranging from 2.4 kHz-73 kHz, depending on the input pumping power. Higher slope efficiency (42%) and shorter Q-switched pulses were obtained for a Q-switched Nd:YAG/Cr⁴⁺:YAG diffusion bonded laser. A comparison of the codoped Cr,Nd:YAG laser performance, with that of a diffusion bonded laser is reported and analyzed.

In this work, together with the laser dynamics and for the first time, the study of upconversion processes that produce violet and visible emissions in yttrofluorite mixed crystals with 15 wt% of YF₃, and 1, 4, 8, and 16 wt% of NdF3 is presented. Site-selective excitation of Nd-doped yttrofluorite crystals by using spectrally narrow pump pulses have shown that it is possible to lase these materials in a single line at 1054 nm or at 1063 nm independently, or simultaneously in both lines depending on the Nd³⁺ concentration and the excitation wavelength. The upconversion measurements were conducted in such a way that the dynamics of the violet and visible fluorescence was performed under lasing and nonlasing conditions. The dynamics of the upconverted emission shows that both energy transfer upconversion and excited state absorption of the laser emission occur.

Laser, operating in the range of 1-2 μm (NIR), is currently an attractive candidate for various applications include ranging, 3D scanning laser radar, communication and other areas where human contact with the laser radiation is possible. The present work is focused on application of PbSe or PbSe/PbS semiconductor nanometer-sized crystals (NCs) for passive Q-switching of NIR laser. Owing to narrow band gap and large exciton Bohr radius of the bulk materials, the NCs of PbSe and PbS acquire unique properties: The quantization effects are strongly pronounced in PbSe and PbS NCs, the strong quantum confinement is thus easily obtained, and the ground-state absorption edge can be tuned over a wide wavelength range (from the visible to infrared). The NCs gain properties of saturable absorber, which allow using them as optical switches. We propose a colloidal synthesis procedure for the preparation of size-selected NCs, suitable for Q-switching of NIR laser. Colloidal synthesis allows simple control over the size of the crystals, and therefore, provides a possibility to produce the samples with desired absorption band position. This method is also very effective for stabilization of NCs and a passivation of their surface with the help of organic ligands.

Composite laser devices of passively Q-switched Nd:YAG were prepared by optical contacting of a Ca,Cr:YAG crystal onto a Nd:YAG wafer, followed by thermal treatments at elevated temperatures. Thermal treatments of the composite devices under reducing and/or oxidizing environments enabled to control the Cr⁴⁺ ion concentration, which affects its absorption saturation behavior. Optical absorption saturation measurements on partialy reduced Ca,Cr:YAG crystal revealed that residual absorption of the saturable absorber at 1064 nm results from excited-state absorption. Laser damage measurements at the gain/absorber interface of the monolithic device showed that the damage threshold at the gain/absorber interface of the composite device is higher than at the entrance interface. The high optical quality device thus obtained was end-pumped by a fiber-optic-coupled diode laser, and exhibited a high repetition-rate oscillations of short pulses, with fair beam quality.

Microscale to nanoscale ferroelectric domain engineering of a near-stoichiometric LiNbO₃ crystal was investigated by using a scanning force microscope. The single crystal LiNbO₃ was grown by the double-crucible Czochralski method with automatic powder supply system. The electric field required to inverse the polarization direction of the domain was about one-ninth of the filed for a conventional congruent LiNbO₃. The near-stoichiometric LiNbO₃ crystal fixed on metal substrate was polished to a thickness of approximately 5 μm. Polarization directions of the domains were locally inverted by applying voltages with a conductive cantilever of the scanning force microscope. Furthermore, the domain structure was patterned in the LiNbO₃ samples, where the domains were inverted by scanning with the cantilever on the sample while applying voltages.

Linear and nonlinear refractive index, Abbe number, electronic energy gap and oscillator strength are reported for a new series of (Mg, Ba)F₂-based fluorophosphates glasses (MBBA system) doped with rare earth dopants (Er³⁺, Nd³⁺) in the concentration range of 6.67×10²⁰ - 2.86×10²¹ (ions/cm³) and 2.5×10²⁰ - 1.25×10²¹ (ions/cm³), respectively. The linear refractive index is found to increase with increasing dopant concentration, while the Abbe number is found to be remarkably concentration invariant, i.e., around 66-68 for both dopants. The average electronic band gap is also found to be almost dopant concentration independent, i.e., about 4.1, while the electronic oscillator strength is found to slightly increase with increasing dopant concentration, i.e., from 6.2 to 6.4. The nonlinear refractive index is found to show a linear increase from 1.2866 to 1.4018 for the investigated dopant concentration range. Those results strongly suggest the present new series of glasses can be excellent laser hosts.

Spectroscopic techniques have been the most sensitive ones to register data with an unparalleled accuracy. The technique of Fabry-Perot Scattering Studies using a FP etalon coupled with a He-Ne laser and a spectrometer is used for characterization of thermotropic liquid crystals. Mesophase transition temperatures have been determined for a wide range of liquid crystals[LCs] which includes nematic, smectic, cholesteric as well as ferroelectric and antiferroelectric LCs. New mesophase transitions have also been detected and classified in addition to those reported by earlier workers. These findings have been corroborated for the same samples using Differential scanning calorimetery [DSC]. A comparison of the observations and the results obtained by FPSS and those obtained by DSC clearly indicates the success of the Fabry-Perot technique in determining the transition temperatures. It is also a clear pointer to the superior sensitivity of the FPSS method. The importance of the FPSS technique lies in its ability to determine with ease the transition temperatures more accurately and with a better sensitivity because it enables us to register even those mesophase transitions which require very small heats of transitions endothermic /exothermic) for their occurrence. The mesophase transitions involving such small heats of transitions tend to be missed out in DSC. This paper gives a complete review of the samples investigated to date using this technique.

The ZnSe single crystal with 8×7×0.8mm in size was grown directly from commercial grade high-purity elements, zinc(6N) and selenium(5N), by the CVT method. The chemical transport agent of (NH₄)₃ZnCl₅ and the growth temperature of 1001~1005° C were employed. The ZnSe crystal shows only (111) face. The FWHM value of double crystal rocking curve of as-grown ZnSe slice was 50s due to the influence of free dendrite crystal microscope on the surface of ZnSe slice, which was in good agreement with the RO-XRD FWHM value of 48sec. The photoluminescence spectrum of the as-grown ZnSe crystal consists of a DAP emission and a broad SA luminescence band. The average etch pit density was about (5~8)×10⁴cm^-2. The infrared (IR) transmission spectra and ultraviolet absorption measurement indicated that the ZnSe single crystal has good crystalline perfection and high optical quality. All the results confirmed the superiority of this CVT growth method for ZnSe single crystal.

Mechanical properties of glassy selenium and selenium based IR chalcogenide glasses Se₅₅As₄₅, Se_67.5As₂₀Ge_12.5 and Se₅₇I₂₀As₁₈Te₃Sb₂ were first studied using dynamical mechanical analysis (DMA). DMA method gave the valuable information about complex Young's modulus of the glassy materials. In parallel with the study of mechanical properties of pure Se and Se-based IR glasses there also has been cleared the character of the glass transition process. The results of DMA study were compared with data obtained by differential calorimetry. The glass transition temperature, established by calorimetric measurements is lower than the temperature, which corresponds to peaks of the loss tangent for all kinds of materials under study. Activation energies of relaxation processes in IR chalogenide glasses were calculated using DMA data.

A low power beam of He-Ne laser light is scattered from the sample of liquid crystal at various temperatures and is made incident on a fixed cavity Fabry-Perot etalon. Analysis of the change in the diameter of the Fabry Perot rings is indicative of the change in the mesophase of the LC. This spectroscopic technique of FPSS has enabled us to determine the mesophase transition temperatures of a wide range of liquid crystals. The technique has now been applied successfully to detect the phase transition temperatures of the biphenyl-based ferroelectric liquid crystals. These findings have been corroborated by the analysis of the thermal runs of the same samples using differential scanning calorimetery. A comparison of the observations and the results obtained by the two techniques is presented. This study clearly indicates the success of the Fabry-Perot technique in determining the PTTs. The FTIR analysis of the same samples is also presented here.

The semicarbazone of p-dimethylamino benzaldehyde (SCPDB) is a potential organic nonlinear optical material. SCPDB has been synthesized and the solubility studies were carried out in the temperature range 30-60°C. Following the slow evaporation technique, single crystals of SCPDB have been grown and the unit cell parameters have been evaluated by single crystal x-ray diffraction technique. The UV-Vis-NIR transmittance spectrum was recorded in the range 200-1100nm. Fourier transform IR and Fourier transform Raman spectra were recorded in the range 400-4000 cm^-1 and the characteristic vibrational frequencies of the functional groups present in the system have been assigned. Second Harmonic Generation efficiency measurements were carried out using Nd:YAG laser.

Stimulated emission in Nd_0.5La_0.5Al₃(BO₃)₄ ceramic random laser was studied at different diameters of the pumped spot d. The developed heuristic model adequately describes the dependence of threshold pumping energy density versus d at d greater or equal to 150 micrometer. At small pumping beam diameter (less than 100 micrometer), very bright and strongly localized emission spot was observed in the center of the pumped area. The spectrum of the bright-spot emission appeared to be similar to that of 'continuum wave' light sources.