Microscopic fluorescence imaging and time-resolved Raman scattering are employed to investigate the effect of high power 355 nm laser irradiation on preexisting and transient defect populations in KH₂PO₄. Defect clusters in the bulk of KDP crystals are imaged with 1 micron spatial resolution using their NIR emission. The intensity of the emission clusters varies widely within the image field. The exposure of the crystal at high power 355 nm, 3 ns laser irradiation leads to a reduction of the number of observed optically active centers. In addition, time resolved Raman scattering was employed to study the transient generation of defects during high power 355 nm laser irradiation.

We have developed a simple method for measuring damage threshold of KTP crystal for CW irradiation using an Argon laser. The experimental results show that there are two types of optical damage in KTP crystal depending on the polarization of the incident laser beam. One type of optical damage corresponds to gray tracks that will be formed when the polarization is perpendicular to the z-axis. Another one is invisible damage that will be formed when the polarization is parallel to the z-axis. In addition, we also observed photorefractive two-wave mixing in KTP crystal under each of the above two polarization states. Our experimental results imply that there exists charge drift during the process of optical damage at both of these polarization states, but the mechanisms are different at these two orthogonal polarization states. After analyses, we believe the first type of damage is due to the formation of Ti³⁺ centers and the second one is due to the drift of K⁺ ions.

Periodically poled KTiOPO₄ (KTP) wafers with short period length are required for generation of green and blue coherent light. Electric field poling processes developed for producing inverted micrometer scale domain structures in other ferro-electric materials cannot be directly applied to flux-grown KTP due to its relatively high (super ionic) conductivity at room temperature. In this paper we describe the low temperature method developed by us for poling flux- grown KTP crystals without modifying their composition. High voltage switching pulses were applied to KTP samples at a temperature below the superionic insulating transition and the switching charge was continuously monitored. This way, high quality domain gratings of 3.8 - 10 micrometers periods were fabricated in 0.5 - 1.0 mm thick flux-grown KTP plates. Second harmonic generation in the range of 400 - 530 nm light by these samples were tested with different types of IR lasers including diode, diode pumped solid state and fiber lasers. The results demonstrate that the low temperature poling technique can provide high quality, short period periodically poled KTP for blue and green coherent light generation.

An investigation of the electric field poling characteristics of RTA, KTA, CTA, and mixed crystals thereof has revealed a number of behaviors, which vary considerably among the arsenates. Sample crystals were studied using piezoelectric mapping, impedance spectroscopy, transient charge transfer measurements and hysteresis loop analysis. Measurements were carried out over temperatures ranging from 20 degree(s)C to 400 degree(s)C. Both parallel plate and lithographically patterned periodic structures were used in this study. Large differences in electrical impedance, coercive field, and hysteresis were observed for various compositions and temperatures. These behaviors have profound implications with regard to the formation of periodically inverted ferroelectric domains for nonlinear optical applications. Tentative theories are presented to explain the differences in terms of crystal structure. Several periodically poled devices were fabricated from the arsenates and operated satisfactorily as Nd:YAG pumped near IR optical parametric oscillators.

In nonlinear optics applications employing quasi- phasematching, short pitch domain gratings are generally required for the generation of visible and ultraviolet light. The conventional electric-field poling method enables the fabrication of periodically-poled lithium niobate (PPLN) down to generally 6 micron-pitch domains in 0.5-mm-thick substrates. While such PPLN is useful for first-order second harmonic generation (SHG) of green wavelengths, shorter periods for blue and UV SHG have been difficult to obtain in 0.5-mm-thick substrates. Here we describe an enhanced electric-field poling technique for ferroelectric materials which utilizes spontaneous flip-back towards high-resolution and high-yield domain patterning.

The effects of reduction, oxidation, Li-enrichment and impurity on LiTaO₃ crystals were studied. It is demonstrated that the best LiTaO₃ crystals show less absorption than LiNbO₃, less photorefraction and no green-light-induced infrared absorption.

Ultraviolet laser emission at 355 nm has been demonstrated using a compact assembly of 3%Nd:YVO₄, KNbO₃, BBO and undoped YAG crystal etalons. The single crystal etalons are polished and optically contact bonded together with precise crystallographic alignment. Thin film coatings with high reflectivity at 1064 and 532 nm and with high transmission at 808 and 355 nm are deposited on the exterior surfaces of the crystal assembly. The generation of 355 nm laser light is achieved using BBO cut for critically phase matched, Type II sum frequency mixing of 1064 and 532 nm laser light at room temperature. The 1064 nm laser emission from Nd:YVO₄ is optimally converted to 532 nm using KNbO₃ cut for Type I, critically phase matched SHG at room temperature. This results in mutually orthogonal, highly polarized 1064 and 532 nm laser light, suitable for efficient Type II conversion to 355 nm in BBO. The water sensitive BBO polished surfaces are wholly protected on both sides with undoped YAG. Over 200 (mu) W CW of 355 nm laser light was obtained using a 1 watt 808 nm pump diode. Additional experiments were performed with devices comprised of KTP and BBO for comparison. UV output power was increased through metallization which improves thermal management of the devices. Composite assembly architecture and operational characteristics are reviewed.

We have constructed a single ring to resonantly double an 18 watt Nd:YLF mode-locked laser and re-double the stored green to produce over 4 watts of power in the ultra-violet. This laser is used to produce a beam of 470 MeV gamma-rays by Compton backscattering the laser beam from 2.8 GeV electrons stored in a synchrotron. Achieving high luminosity of the colliding beams requires very good mode quality and beam stability at the intersection point 22 meters from the laser. The ring consists of six mirrors, with two 25 cm radius of curvature mirrors enclosing each nonlinear crystal. The drive laser is a lamp-pumped Nd:YLF with a 50 ps bunch length at 76 MHz. A pointing stabilizer servo has been constructed as part of the infrared (IR) mode matching telescope. The IR to green conversion is accomplished in a 15 mm long non-critically phased matched LBO crystal located at a 40 micron waist, with an IR conversion efficiency of 70%. A stable, nearly diffraction limited UV beam of up to 4.2 watts is generated in a BBO crystal in the green storage ring. The output power is relatively independent of the efficiency of the LBO and BBO crystals. This fact makes it possible to reduce the amount of non-TEM₀₀ modes created by walk-off of the UV by using relatively thin BBO crystals. At present, however, the lower bound on the BBO thickness is limited by the loss of conversion efficiency at high power.

New faster detection systems have allowed better measurements of complex fluorescence decays for active ions in laser crystal materials. We have measured a fluorescence decay that shows a fast initial decay followed by a non- exponential behavior that cannot be described satisfactory by most standard models for nonradiative energy transfer process. With current models it is customary to consider three characteristic temporal stages for the luminescent decay: (1) an exponential decay that is described by the first order approximation of the corresponding model at very short times, (2) a non-exponential decay described by the model at intermediate times, and (3) an exponential decay at later times determined by the migration excitation among donor ions. A new model is presented to account for the donor transient with no temporal stages. The master equations are solved in an analytical and exact form. This modeling allows us to consider any sum of interactions to drive the direct energy transfer. The discreetness of the crystal lattice is not neglected and it is taking into account the actual random distribution of activators around each donor. By using our modeling we are able to predict the measured fluorescence decay of the ⁴F_3/2 state of the Nd⁺³ in Nd(1.5%),Er(20%):YSGG.

A novel noise-insensitive optical interferometric technique has been developed for highly scattering environment, using photorefractive coherence grating. Two-wave mixing process in a photorefractive barium titanate crystal effectively reduces scattering noise, and we have successfully detected interferometric signals through scattering media of up to 17 mfp, with a high visibility. We have also demonstrated two- dimensional thickness measurement of an optically scattering thin film using our new interferometry.

We demonstrate an adjustment-insensitive technique for measuring the squared temporal coherence function of cw, longitudinally multi- and monomode semiconductor lasers, using codirectional two-beam coupling in photorefractive InP:Fe and CdTe:V crystals. The emission spectra of the diodes are measured independently and the coherence functions are also calculated by Fourier transform from the spectra. The photorefractive measurements are in good agreement with these calculations. The coupling of two partially coherent waves in low-speed absorptive photorefractive media is studied. We give an exact explicit solution of the 1D linear coupled wave equation for the beam intensities and for the degree of mutual coherence, which changes during the wave mixing. This change is significant for large input beam intensity ratios but only in second order in the coupling strength for equal input beam intensities. In this latter case for moderate coupling strength the energy transfer between the beams is proportional to the square of the input coherence degree, providing a simple determination of the squared coherence function due to measurement of the signal intensity enhancement as function of the time delay between the beams. The possibility to determine some important characteristic of the emission spectrum from the measured squared coherence function is discussed.

The third-order optical nonlinearity of a series of new conjugated silicon-ethynylene polymers, poly(aryleneethynylenesilylene)s, have been studied by using the degenerate four-wave mixing technique. The fast nonlinear optical susceptibilities of the polymers containing various groups were determined for the solutions in chloroform, tetrahydrofuran and toluene. The electronic and nuclear contributions of the (chi) ⁽³ susceptibility and the thermal nonlinearity of the solutions were separated. The (chi) ⁽³ susceptibility of the polymer containing tetracoordinate Ph₂Si groups was found to be comparable with those of the best polymers.

CW diode pumped solid state lasers have sought for various scientific, medical and military applications, where compact reliable, stable, and highly efficient sources are desirable. There are several applications such as fiber- optic sensing or range finding which require short bursts of high peak power densities at multi-kilohertz repetition rates, and with a good beam quality. An extensive research on the properties of passively Q-switched, CW diode-pumped, ND-lasers has been conducted. We have used various pumping schemes to diode pump the Q-switched Nd:YAG and Nd:YVO₄ laser crystals. Such schemes are transverse pumping by a cylindrical microlens-coupled diode array or longitudinally pumping by a fiber-coupled diode array. The passive Q- switching elements were Cr⁴⁺:YAG (polished, uncoated) and Cr⁴⁺:GGG (polished, coated), which were inserted inside the laser resonator. The 1.06 micrometers laser emission shows a repetitive modulation in the kHz frequency domain, and temporal bandwidth, full width at half maximum, in the range of 50 - 600 nsec. The modulation frequency and bandwidth depend on the characteristics of the Q-switching material (e.g. Cr⁴⁺ concentration, sample thickness) and on the input power level of the diode array used. We shall report design parameters and performance of various types of passively Q-switched and free-running diode pumped Nd-lasers. We shall present and discuss methods to increase the efficiency of Q-switched solid state lasers.

Real-time holography is a fast-developing technique for correction of dynamic and static aberrations in imaging telescopes. In this paper a novel schematic of recording the hologram is discussed based on the use of phase conjugation for compensation for dynamic distortions in the real-time hologram. This technique can improve significantly the quality of the corrected image of remote objects and allows to use optically inhomogeneous materials for recording the real time hologram and segmented design of the holographic corrector.

The state of the thin axial symmetric elastic mirror under deformation tension is considered in approximation of the thin membrane theory. The solution of the equations is presented here describing the mirror's distortions under both the pressure applied across the film and the stretching forces along the film. To study optical quality of the flexible mirror's surface, the calculations were performed of energy angular distribution of the reflected radiation (for incident plane-front beam) in the focal plane of the elastic mirror.

BBO crystals were grown by the top-seeded solution growth technique from a Na₂-O melt-solution. Optimization of heating conditions and technological growth parameters allowed us to produce high-quality optic crystals. Their main morphological feature is the facing of a boule side surface. The area of hexagonal prism face {1120} can reach several square centimeters. Non-linear-optical elements which are produced from a crystal with well arranged faces have higher coefficients of laser radiation frequency conversion. The BBO crystals were studied for linear and non-linear absorption. Linear absorption was measured with conventional spectroscopic method. The analysis of supplementary absorption spectra and thermally- stimulated luminescence behavior allowed us to suggest that Na atoms are a main spontaneous impurity in BBO crystals providing supplementary absorption in UV-region. We used the 4^th and 5^th harmonics of Nd-YAG laser to measure the non-linear absorption. The selected optimized crystals were used in various optical schemes up to the 5^th harmonic generation. Harmonic generation was studied by high performance original Nd-YAG laser (SLM-operation, D. L. output beam up to 100 Hz repetition rate, 1.8 ns pulse duration, 16 W output). Harmonic efficiency values are listed below. Several optical schemes for harmonic generation are discussed.

CsLiB₆O₁₀ (CLBO) is a highly promising nonlinear optical material. However, its application is limited due to the difficulties in producing optically uniform CLBO crystals. High viscosity of Cs₂O-Li₂O-B₂O₃ melt retards both natural and forced convection in the melt. With the goal to improve the heat and mass transfer in the melt, the study of crystallization in the Cs₂O-Li₂O- B₂O₃-MoO₃ system was carried out. The CLBO crystals 60 X 40 X 20 mm in size grown using LiCsMoO₄ as a solvent were found to be free of cracks, bubbles, and inclusions. Nonlinear optical parameters and physical properties of those crystals turned out to be similar to those reported before. Mohs' hardness is 5.5, transparency window ranges from 0.18 to 2.7 micrometers , nonlinear coefficient is 1 pm/V, angular and spectral bandwidth of synchronism are 0.5 mrad-m and 0.1 nm-cm. The walk-off angle is 2 degree(s) at 0.53 micrometers . The nonlinear optical elements for the 4^th harmonic of Nd:YAG laser were fabricated and tested.

Second harmonic generation (SHG) of 532-nm radiation from 1064-nm radiation in LiNbO₃ doped with 0.6 mol% MgO has been investigated by using pulsed Nd:YAG lasers whose pulse duration is less than 25 nanoseconds. Efficient and noncritically phase-matched SHG has been achieved at room temperature without any severe photorefractive problem. SHG conversion efficiency of 50% was typically obtained with a 9.5-mm-long crystal and a fundamental peak-power density of 22 MW/cm² and 0.8 GW/cm² when the pulse duration of Nd:YAG laser are 25 ns and 40 ps, respectively. It was found that thermal heating due to a linear optical absorption and nonlinear intensity-dependent absorption cause a saturation of conversion efficiency for SHG with nanosecond and picosecond pulses, respectively. It is also observed that photorefraction occurs when the intensity of a fundamental laser is higher than 4 GW/cm² only for SHG with picosecond pulses. These experimental results show that LiNbO₃ doped with 0.6 mol% MgO is one of the best nonlinear optical crystal for an application to SHG with pulsed Nd:YAG lasers.

The severe requirements are posed on nonlinear phase conjugation (PC) mirrors with using those for compensation of laser beam aberrations in turbulent atmosphere at large distances. These requirements are connected with high losses of a laser-illuminator radiation due to atmospheric beam spreading and also with strong modulation of phase and intensity distribution in the beam being conjugated. To specify these requirements we present in this paper results of numerical simulation of the process of PC correction of atmospheric distortion. The simulation was carried out for various parameters of an atmospheric range and various radiation wavelengths. It was shown that in the case of strong turbulent scintillation the PC compensation allows one to increase the beam intensity by three orders of magnitude. The beam energy delivered to the receiver is close to that delivered in absence of turbulence if turbulent inhomogeneities of high spatial frequency are resolved by transmitter. The requirements to the PC mirror are formulated for the angle of view, reflection coefficient, reproduction fidelity, etc. The influence of saturation effects in a laser amplifier on fidelity of atmospheric distortion compensation is analyzed.

Boundaries of the electric macrotwins (antipolar parts of crystal) have always been found in X- or Y-axis crystals. Boundaries are nearly planar and located in subseed zone of crystal along the (00.1) plane. In large crystals two more of such boundaries are usually found at a distance of 15 - 18 mm in both sides from the central boundary. In Z-axis crystals, boundaries of macrotwins have never been found. There are only microtwins up to a few mm in size and insuperable tendency to cellular breakdown across the entire growth interface of crystals after 15 - 30 mm of growth. When Na₂O and NaF are used as a solvent, antipolar microtwins can be found near macrotwin boundaries or cellular growth zone and in the whole volume of crystals, respectively. In the latter case, crystals are stressed and show a partial fracture along the (00.1) plane. Misoriented blocks and low-angular boundaries can be found at the growth stages later than seeding and growing up to the required sections. Most of the inclusions in BBO crystals are of flux type with a partially void space and a soli state core. If reactions of synthesis had not been finished before melting, enormous amounts of CO₂ and probably some amounts of OH were detected, along with near eutectical alignment of Ba and Na in the core of inclusions. Possible causes of formation of the above-mentioned features in BBO structure are discussed.

Theoretical treatment of the effects of external pulse field on the emission and absorption of two impurity centers has been attempted. Good overlapping of emission band of one center (donor of energy) with the absorption band of another center (acceptor of energy) is assumed, so that radiative and non-radiative energy transfer may take place. Mathematical model is based on the system of reduced Maxwell equations for magnitudes of field components and Bogolubov's equations for elements of multiparticle density matrix of donor-acceptor complex. Numerical solution is obtained for NaCl:Cu, Mn and KCl:Pb,Eu crystals. These materials are differing in the value of transition dipole moment of acceptor absorption. It is low for the first medium while for KCl:Pb,Eu it is comparable to that one for the donor emission. It turns out that in the case of low value of transition dipole moment the luminescence of both components of donor-acceptor pair takes place. On the contrary, only acceptor emission exists in the case of high value of transition dipole moment of acceptor when the pump intensity is low. Simultaneous luminescence of donor and acceptor occurs when pump intensity is enough. So, in the systems of such kind the emission may be changed over from one frequency to another through the power level of pump radiation.

The nonlinear optical properties were measured for two high- refractive-index glasses to obtain a general description of the n₂ dispersion for wide-bandgap dielectrics and to select a new reference material for CS₂ which shows pulse-width dependent n₂. We determined the n₂ values of the glasses by Z-scan method in visible region using femtosecond lasers and the values in near infrared region by THG method. We used the n₂ value of fused silica as a standard that was determined precisely from reliable second-order nonlinear constants through two- consecutive cascading process. Dispersions of n₂ were found dominated by two-photon absorption (TPA) and fitted with the empirical equation obtained for semiconductor materials in the longer wavelength region above TPA edge. For shorter wavelength region, discrepancy was observed between calculated and measured values. We also measured the n₂ values using THG, DFWM, Z-scan, and Kerr-shutter methods with different pulse widths and repetition rates. It was found the values coincided well among the methods while CS₂ showed strong dependence.

In this paper, we reported, for the first time to our knowledge, that polycrystalline germanium-dioxide has a n < 1 and the extinction coefficient becomes smaller than other materials given at 10.6 micrometers , n is 0.27 and K is 0.51, we also exactly measured the infrared reflective spectra of polycrystalline germanium-dioxide from the input angle 20 degree to 70 for wavelengths between 2 and 25 micrometers . Our measuring results are compared with an exact calculation, and the agreement is found to be excellent. On the other hand, in order to study on the properties of polycrystalline germanium-dioxide for the materials of hollow-core fiber in detail, we fabricated a hollow-core fiber by use of this material. After then, we measured the straight optical fiber losses, the transmission properties of the bending fiber and the spot size of the fiber's output beam, we found that the high order mode degenerate quickly with the increase of the length and the nonuniform in the structure of fiber causes the loss of all kinds of modes. We further found that the different focal length of coupling Len causes different bending loss and the diameter of the output beam depends strongly on the existence of transmission mode in the fiber, meantime, the transmission rate of fiber depends strongly on the divergence angle (theta) .

The vibrations of phosphate (PO₄^-3) ions in single crystals of hexagonal Ba₅(PO₄)₃F have been investigated by means of polarized Raman scattering and compared to Raman frequencies observed in fluorapatite analogs Sr₅(PO₄)₃F and Ca₅(PO₄)₃F. The Raman vibrational frequencies decrease upon substitution of Ba²⁺ for Sr²⁺ or Ca²⁺ in the lattice, asymptotically approaching the Raman frequencies for vibrations of the free ion. The observed splitting is in accord with predictions made by a group theory analysis of the factor group of the unit cell. The effects of the host lattice environment on the magnitude of the Davydov splittings and frequency shifts of phosphate ions within different crystals with the fluorapatite structure are demonstrated to be inversely proportional to the unit cell volume.