Quasi four level lasers, such as the Ho:Tm lasers, have more physical processes associated with production of laser radiation than the more common four level lasers, such as the Nd lasers. Energy transfer processes, including up conversion and self quenching, as well as the existence of a nonnegligible thermal population in the lower laser level can be largely neglected in common four level lasers but are highly important in quasi four level lasers. Implications of these physical effects are explored with an emphasis on the Ho:Tm laser system.

The small signal gain coefficients of Ho:Tm:YLiF₄ (Ho:Tm:YLF) have been measured as a function of pump energy fluence and Ho concentration, in order to determine the optimum conditions for efficient pulse amplification. The results show that, for Ho:Tm:YLF amplifier systems, the available pump energy fluence ultimately dictates the Ho concentration.

A flashlamp pumped Ho:Tm:LuAG laser, using Tm as the only sensitizer, has been demonstrated. Most flashlamp pumped Ho lasers utilize either Er or Cr as the major sensitizer while Tm acts as an intermediary in the energy transfer process to Ho. In this case, Tm serves as both the major absorber and transfers the absorbed energy directly to Ho. By evaluating this particular combination of dopants, the contribution of the various Tm manifolds to the pump process can be determined.

Significant enhancement of the thermal loading capability has been achieved with both Er³⁺ and Nd³⁺ doped inherently strong glasses by an ion-exchange chemical strengthening process. A free running laser with an average output power of 6.5 W and a Q-switched single mode laser with an energy of 5 mJ at a repetition rate of 15 Hz have been demonstrated at the 1.54 micrometers eye safe wavelength with strengthened QX/Er glass. An average output power of 110 W at 1.05 micrometers has been obtained employing a strengthened QX/Nd glass rod.

Divalent uranium doped CaF₂ Q-switch has been tested as a saturable absorbing Q-switch. Laser output at 1535 nm with 10 mJ of energy and a 60 ns pulse width was demonstrated at 8.5 Hz by using U²⁺:CaF₂ as a saturable absorbing Q-switch. The laser media is QE7S and experimental Er:glass, designated QX/ER.

Time-Resolved Laser-Induced Fluorescence (TRLIF) is a very sensitive and selective method that has been used for actinides and lanthanides analysis in the nuclear fuel cycle. This technique has been used in different fields such as in geology, in the Purex process, in the environment, in the medical and in waste storage assessment. Spectroscopic data, limits of detection and results obtained in previously quoted fields are presented.

We report here on a novel Color Center Laser (CCL) optical construction, providing two unique regimes of generation: (a) a simultaneous generation across the whole emission region of the LiF:F₂^- active medium (1.1-1.24 micrometers ) with efficiency of 15% and a simultaneous frequency doubling in the visible green-red spectral region (0.55-0.62 micrometers ); (b) a regime of multi frequency lasing with a special preassigned spectral distribution or spectral coding by means of placing a special mask or image controller into the pump beam.

A Ti:Sapphire CW laser operating at room temperature provides an output power of 6.7 W, limited by available pump power. A Z-configuration oscillator (LEXEL laser) was modified to operate in dual pump mode. The Ti:Sapphire laser was pumped by two independent 13 watt CW Ar-ion lasers. The two Ar-ion lasers were focussed on each end of the Ti:Sapphire crystal. The Ti:Sapphire laser covers the visible red to the near infrared regime (690-1100 nm) with four sets of mirrors. A three plate birefringent filter was used for wavelength tuning, with a 0.5 nm bandwidth. The spectral analysis was performed with a monochromator with a resolution of 0.2 nm. A maximum output of 6.7 Watt was achieved at 790 nm, in TEM₀₀ mode, corresponding to a conversion efficiency of 26%. The Ti:Sapphire was operating below saturation levels at 26 W total pump. Laser output without the birefringent filter resulted in spontaneous mode hopping leading to output wavelength fluctuations between several resonant wavelengths. Double pumping resulted in higher output powers than single pumping with corresponding total input power. The flat tuning curve in combination with the high output powers makes this laser an ideal source for spectral investigations of laser tissue interaction.

ABCD transfer matrix theory was utilized to study the stability of a solid state laser with a Brewster-angle-cut active medium in a Z-fold cavity consists of two spherical and two flat mirrors. Analytic solutions of stability regions for CW operation have been obtained. These solutions allow easy analysis of the behavior of the stability regions when the resonator parameters are varied.

We investigated the fluorescence and lasing characteristics of chromium- doped forsterite with high chromium concentration of 0.13-0.14 mol%. It was shown that the 0.13-0.14 mol% chromium sample has about threefold stronger intensity of the fluorescence extending from 1050 nm to 1400 nm, which causes laser oscillation, than the 0.04-0.06 mol% chromium sample which is usually used. The strong polarization of fluorescence extending from 1050 nm to 1400 nm was observed. Laser oscillation was achieved by using the 0.13-0.14 mol% chromium sample whose size was only 5 X 5 X 5 mm³.

Devices incorporating multiple frequency-conversion stages within the cavity of an optical parametric oscillator can be used to extend the tuning range of the OPO or to improve its performance. We have used plane-wave theory to identify operating regimes of a number of such devices which have a large dynamic range of high efficiency. We have also carried out more detailed multidimensional numerical simulations of these regimes. By way of illustration, we discuss simulations of a high- gain device called the OPO-OPO.

The effect of the pump, signal, and idler wave phases on three-wave nonlinear parametric mixing is investigated in a series of single-pass- gain experiments. Measurements are made with two angle-tuned KTP crystals in a 532 nm pumped, walkoff-compensated, optical parametric amplifier that is seeded by an 800 nm cw diode laser. In one of the measurements the second crystal is orientated to have its effective nonlinearity d_eff. of opposite sign to that of the first crystal, so that all mixing that occurred in the first crystal is canceled by the second when the phase mismatch (Delta) k_{crystal 1} equals (Delta) k_{crystal 2} equals 0. Efficient two-crystal amplification is subsequently restored by selecting the correct phase relationship for the three waves entering the crystal by inserting a dispersive plate between the crystals. The experimental results are explained in a straightforward manner with diagrams involving the three input wave polarizations. These results demonstrate that walkoff-compensated geometries require phase correction to achieve efficient mixing in the second crystal whenever the nonlinear interaction involves two extraordinary waves (e-waves). One practical application of this work may be lower oscillation thresholds and enhanced performance in walkoff- compensated optical parametric oscillators which use two e-waves.

We report the experimental study on a intracavity frequency doubling and self-Q-switching phase-conjugation two-rod Nd:YAG lasers, using a KTP crystal as second harmonic generator, and a phase-conjugation mirror based on stimulated Brillouin scattering in acetone. The experimental results show that this kind of lasers not only generate Q-switched laser pulses, with duration about 15 ns, and energy over 90 mJ at 532 nm, but also possess the capacity of stabilizing the laser pulse energy, which the energy fluctuation about 5% are obtained. Theoretical analysis on the experimental results is given.

We have built a cw, diode-laser-pumped, Nd;YAG slab laser that emits 72 W of multimode power when pumped with 235 W, or 40 W of TEM₀₀ power when pumped with 212 W of diode laser power. The slope efficiencies are 36% for multimode operation and 22% for TEM₀₀ mode operation. The laser uses the zig-zag slab geometry to reduce the thermal effects associated with high power operation, resulting in less than one wave of distortion at the full pump power. Reasonable efficiency for the side- pumped slab design was obtained by confining the pump power within a gold-coated box which surrounds the slab. TEM₀₀ mode operation was obtained in a simple three-mirror folded cavity. The Nd:YAG slab acted as an aperture in the cavity and the astigmatism due to off axis incidence on a curved mirror corrected for a minor 1 meter cylindrical thermal lens. A significant advantage of our design over previous slab lasers is a new Teflon AF protective coating on the slab total internal reflection surfaces which greatly simplifies the mounting and cooling of the slab laser medium.

We report on diode laser side-pumped, cw Nd:YAG rod lasers operating at pump powers up to 1 kW. With linear diode laser arrays as pump sources a pump power of 90 W/cm is realized. In multimode operation at 1064 nm, output powers of more than 300 W cw are observed. Applying a dynamically stable resonator design, an output power of more than 45 W in TEM₀₀ mode operation is realized with an optical-to-optical efficiency of more than 11%. Higher pump powers up to several 100 W/cm can be achieved by using fiber-coupled diode lasers as pump sources. Laser performance, thermal properties and possible applications of these laser systems will be discussed.

The reliability of high power continuous-wave (CW) 1 cm monolithic AlGaAs (808 nm) laser diodes is extensively investigated. Lasers with two total aperture sizes, 1800 micrometers and 3000 micrometers , are life tested at power levels of 10 W and 20 W, respectively for 1500 hours to 4000 hours at 30 degree(s)C heatsink temperature. These lasers exhibit no failures during the lifetests (total device hours of 45,000 hours for the 10 W lasers and 42,000 hours for the 20 W lasers). We demonstrate a mean time between failures (MTBF) exceeding 50,000 hours and a median life (ML) of 40,000 hours for the 10 W laser diode and a MTBF over 48,000 hours and a ML of 13,000 hours for the 20 W laser diode.

This paper discusses the design and testing of the lasers built for the Clementine Laser Rangefinder that was used to map the lunar topology. a baseline Acceptance Test Procedure (ATP) was run once and the flight laser was built. Then the Laser Resonator Assembly (LRA) and the Laser Power Supply (LPS) were subjected to vibration and electromagnetic compatibility (EMC) testing as well as a 50 hour Thermal Vacuum test (T- VAC). Laser energy and boresight stability was checked after each vibration axis and after EMC testing. A complete ATP was run again after all environmental tests were completed, results were compared to baseline.

Passive Q-switching of optical fiber-diode-pumped Nd:GdVO₄ laser by special developed LiF:F2- crystals have been realized. Pulse duration of 15-100 ns and pulse repetition rate of 5-200 kHz have been obtained.

The powerful tunable laser with high output energy is needed for laser spectroscopy, laser chemistry, biology, medicine and other appi icat ion. The result of design of the powerful Nd: glass laser set -up ut ii iz ing process of harmonic generation, optical parametric oscillation, parametric ampl if icat ion under the injection of the seeding radiat, st iinulated Raman scattering all owing to span completely through the spectral range from 1.3 to 0. with the output energy of several J are reported.

We review progress of quasi-phasematched (QPM) optical parametric oscillators (OPOs) in bulk periodically poled LiNbO₃. Using the electric field poling process, we can reliably fabricate 0.5-mm thick crystals with uniform domain structures over 15-mm long. Periodically poled material retains the low loss and bulk power handling properties of single domain LiNbO₃, and QPM allows noncritical phasematching with the highest value of the nonlinear coefficient. OPOs pumped by 1.064-micrometers pulsed Nd:YAG lasers have been operated over the wavelength range 1.45 micrometers to 4.0 micrometers with tuning by temperature or QPM period. We have shown oscillation threshold as low as 0.020 mJ with a Q-switched pump laser, and pumping over two times threshold without damage. We have also demonstrated a doubly resonant oscillator near 1.96 micrometers pumped directly with a cw diode laser at 978 nm.

Difference frequency mixing in KTiOAsO₄ (KTA) of an injection-seeded pulsed Ti-sapphire ring laser and a Q-switched Nd:YAG laser has produced high power output from 2.65 micrometers to 5.3 micrometers .

Mode-locked Er:Cr:YSGG laser ((lambda) equals 2.8 micrometers ) pulses with 100 ps duration were used to pump travelling wave optical parametric generators (OPG) based on ZnGeP₂ and GaSe crystals. In the ZnGeP₂ a tuning range 3.9-10 micrometers was achieved in both cases of type I and II synchronism, OPG pump threshold being only 0.25 GW/cm² for 11 mm long crystal, the smallest reported value for travelling wave OPG. Type II synchronism was characterized by OPG linewidth of 30-40 cm^-1, and conversion efficiency up to 18% corresponding to MW peak power; type I had broader linewidth, especially near degeneracy point. In a double- pass scheme OPG had almost diffraction-limited divergence which allowed to focus radiation into a 20(lambda) diameter spot. In case of GaSe crystal the tuning range was larger: 3.5-18 micrometers , but at the expense of higher pumping threshold-4 GW/cm² for a 10 mm long GaSe crystal; quantum efficiency being 1-2%. Results concerning nonlinear spectroscopy of InSb at room temperature and GaAs/AlGaAs multi-quantum wells near (lambda) equals 9 micrometers , with focussed OPG beam intensities of 10⁴- 10⁸ W/cm² will be also presented.

ZnGeP₂ is a candidate material for tunable mid-infrared optical parametric oscillators pumped by a 2-micron laser. Performance, thus far, has been limited by appreciable optical absorption extending from the band edge near 0.7 micrometers to beyond 2 micrometers . In the present investigation, electron paramagenetic resonance (EPR) and electron- nuclear double resonance (ENDOR) is used to establish the specific identities of the defects responsible for the optical absorption in crystals grown by the horizontal gradient freeze technique. The dominant acceptor, observed by EPR in as-grown crystals, is a singly ionized zinc vacancy (V_Zn^-). Photo-induced EPR provides evidence that the dominant compensating donor is a phosphorus vacancy (V_P⁺). Photoluminescence data and optical absorption spectra are interpreted in terms of transitions between these donor-acceptor pairs.

Advances in diode-laser-based nonlinear blue sources as well as blue injection lasers have generated interest in using these sources for optical data storage. Recording results using a 429-nm, frequency doubled-diode laser are illustrative in understanding the requirement on these laser sources. A very stringent requirement on the laser source is the low cost necessary for high market penetration of the storage device.

This paper presents a study of the optimum design parameters for an optical parametric oscillator as a frequency divider. A minimum threshold for oscillation of 9 mW, for near frequency degeneracy and a total conversion efficiency of 20%, was achieved over a wide range of pumping levels even up to as much as six times above threshold. An optical frequency divider was acquired by phase locking the signal-idler frequency to an external microwave frequency reference.

We report on the generation of powerful, widely tunable fs radiation by parallel operation of two singly resonant optical parametric oscillators. The devices are synchronously pumped by the second harmonic of an additive-pulse modelocked Nd:glass laser, that provides pulse trains of approximately equals 2.5 microsecond(s) and 400 fs pulse duration. As nonlinear crystals in the OPO's we choose BBO specimens (length 5 mm and 5.8 mm, respectively), enabling generation of fs-pulses with further advantages of high damage threshold, high nonlinearity and good optical quality. Small differences of the experimental setup lead to slightly different OPO parameters. For OPO I a single pulse energy of 10 nJ is achieved in a tuning range of 0.9-1.5 micrometers with a pulse duration of 120 +/- 20 fs while OPO II delivers pulses of 200 +/- 20 fs in the range 0.7-1.5 micrometers . Frequency tuning of the OPO's is carried out within a fraction of a second by computer controlled stepping motors, readjusting crystal orientation, cavity length of the OPO and realignment of one resonator mirror. The time jitter is estimated from cross correlation measurements to be +/- 50 fs offering high temporal resolution in pump-probe investigations.

We report on a traveling wave optical parametric generator producing tunable femtosecond pulses between 550 and 590 nm (signal) and between 1230 and 1450 nm (idler). The second harmonic of a 1 kHz repetition rate Ti:sapphire laser/regenerative amplifier system serves as an UV pump source. To achieve nearly bandwidth limited parametric pulses we combine a narrow band seeder with a broad band parametric amplifier. Pulse compression at the idler wavelengths is observed which is attributed to temporal gain narrowing. The optimization of simple seeder-amplifier configurations in the small signal limit at pump wavelength near 400 nm is analyzed with respect to achievable spectral narrowing and pulse shortening in the amplification process.

High power deep ultraviolet (UV) radiation has attracted much attention in areas of photolithography, micro fabrication and material processing as well as ultra high density optical disk mastering. We report progress in quality of (beta) -BaB₂O₄ (BBO) which is essential in obtaining 1.5 W of cw UV generation from the BBO resonant ring cavity out of 3 W of green input power from a diode pumped Nd:YAG laser. Progress in KTiOPO₄ (KTP) and its potential applications are also reviewed.

The formation of gray tracks in KTP is initiated when a Nd:YAG laser produces above-band-gap photons which, in turn, create electron-hole pairs along the beam path through the crystal. These photons result from nonlinear processes (e.g., tripling of the fundamental beam, sum- frequency generation with a fundamental and a doubled beam, etc.). These processes will create 355-nm photons which, coincidentally, nearly match KTP's room-temperature band edge at 350 nm. Many of these electrons and holes produced by above-band-gap photons will recombine; however, a portion of them will be trapped at stabilizing entities such as vacancies or impurities and form 'stable' gray tracks. In the present work, x-rays are used to simulate the effects of an intense laser beam, and thus increase the total number of centers within the sample that are available for study with electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) techniques. In flux-grown KTP crystals, holes are trapped at trivalent iron (Fe³⁺) ions, thus forming Fe⁴⁺ centers, and electrons are trapped on titanium ions having an adjacent oxygen vacancy, thus forming Ti³⁺-V_O centers. At room temperature, the decay of these electron and hole traps has a half-life of approximately 2 hours. Optical absorption bands associated with these electron and hole traps give rise to the gray- track color.

We report on the top seeded solution growth of LBO from an excess of B₂O₃ solution. Parameters investigated included the Li₂O/B₂O₃ ratio, rotation, pulling and cooling rates. Unstable crystal growth encountered, such as hopper growth and inclusions, can be attributed to the high viscosity of the solution, and methods of increasing the forced convection was examined by the melt simulation using the tracer method. With careful control of the above parameters, clear crystals of approximately 40 X 48 X 30 mm have been successfully grown. It was characterized that the grown LBO crystals have good optical homogeneity, no growth striations, no growth sector boundaries, small change of refractive index less than 1 X 10^-5/cm. A bulk laser damage threshold of LBO was determined to be 45.0 GW/cm² at 1.064 micrometers , 1.1 nsec pulse width. This is one of the highest bulk damage threshold of any inorganic nonlinear optical crystal.

We have demonstrated the fabrication and characterization of polymer- based optical waveguides. Reported here is a fabrication technique for polymeric channel waveguides with the inverted-rib structure. The waveguide is consisted of a polymer film spin-coated on the SiO₂/Si substrate, in which channel grooves are pre-patterned to provide lateral optical confinement. Moreover, modal characteristics of the waveguides for a TE-polarized light source at 632.8 nm are also calculated and measured for comparison using the Galerkin's method and the Laser beam analyzer, respectively.

Poor beam propagation is a typical characteristic of most pulsed optical parametric oscillators. We describe the design and operation of a tunable narrow linewidth (< 0.2 cm^-1) high energy (> 100 mJ), low divergence (< 0.5 mrad) OPO system to overcome this problem. Frequency doubling efficiencies of this OPO are 185 when using BBO and 28% in KDP. These high efficiencies are attributed to the use of an unstable resonator in the OPO.

In separate experiments, we performed phase-matched sum-frequency generation (SFG) and phase-matched second-harmonic generation (SHG) of the optical waves inside an optical parametric oscillator (OPO). The OPO is synchronously pumped and is based on AgGaS₂. The pump wavelength is at 1.064 micrometers , and the signal and the idler wavelengths are tunable around 1.319 micrometers and 5.505 micrometers , respectively. Intracavity SFG between the 1.064-micrometers and the oscillating 1.319-micrometers waves produces yellow radiation near 0.589 micrometers ; while, intracavity SHG of the 1.319- micrometers wave generates red radiation near 0.660 micrometers . Several KTP crystals are tried in the SFG experiment. A 8.5-mm long KTP crystal, cut at (theta) equals 79 degree(s) and (phi) equals 0 degree(s), yields a 10.5% energy conversion from the infrared pump to the yellow radiation. A 6.5-mm long KTP crystal, cut at (theta) equals 63 degree(s) and (phi) equals 0 degree(s), generates 12.5% conversion efficiency, and a 13-mm long crystal of the same cut converts 8% of the infrared pump into the visible. In the SHG experiment, a LiIO₃ crystal is used, and the energy conversion to the red radiation is 9.5%. Maximum pump depletion is about 40% in both SFG and SHG experiments. Higher pump conversion is expected at higher pumping levels, and with a less lossy AgGaS₂ crystal, a larger fraction of the depleted energy should be upconverted into useful visible light.

Doping a little Fe₂O₃ and Tb₄O₇ into LiNbO₃, the double-doped crystal LiNbO₃:Fe,Tb was grown by Czochralski method. Its diffractive efficiency and the four-wave mixing phase conjugate reflectivity were measured to be the similar to the single-doped LiNbO₃: Fe crystal. But the response time of the double-doped crystal was measured to be tens seconds, showing a great improvement comparing with LiNbO₃: Fe. The mechanism of the results was discussed by measuring and calculating the values of the photoconductivity.

We present a real-time optical information processing system using a novel geometry of mutually pumped phase conjugate reflection induced by self-pumped phase conjugation of an incident beam in Cu doped KNSBN crystal. Stable parallel image addition and subtraction have been achieved.

Long time testing of laser cavities based on modified Sagnak interferometer (MSI) in various lasers exposed their following advantages: lasing on the main transversal mode and suppression of the higher mode lasing; the high energy stability in pulse regime (unstability less then 1%); possibility of tuning the mode-locked pulse duration (from 2 to 100 ps); exactly longitudinal and counter-running 2- beam laser pumping. Effect of higher transversal mode suppression in laser cavity with MSI was qualitatively explained in 'soft rim aperture' terms early. MSI-cavity with the off-centered lens position is one where the 'soft unstability' is appeared to together with the capability to suppress the high order transversal modes. The resulted laser field in the case is nonsteady-state and the transient time is infinite, the phase trajectory may not be described as reproducible one and Gauss beam parameters q are chaotically skipped inside some region on the complex plane. The most interesting result of the beam propagation in MSI analysis is the strong dependence of the transient time to the steady- state field distribution from the lens position relative to the optical center of MSI. The current application of MSI-cavities of the various lasers and their modes of operation are discussed.

In this paper, the dynamic characteristics of Gaussian resonators with thermal lensing is analyzed and a novel resonator-stable resonators with Gaussian reflectivity mirrors (GRMSR) is introduced. CW lasers with designed Gaussian stable resonator radiates laser beam with output power 200 W and beam parameters 6.2 mm mrad. For Gaussian resonators, the near field shows more uniform distribution and the far field shows lower diffraction rings than those of plane-plane stable resonators.

This paper reports about development of previously described diode- pumped Nd:YAG chip lasers with monolithic ring resonators. We have obtained cw single longitudinal- and transverse-mode operation at the wavelength of 1064 nm. The maximal output power of 80 mW has been achieved at pump power of 500 mW. The laser design features and parameters are described.

The elaborated technology of laseral optical pumping is successfully used for the purification of fibers from impurities. This is the novel and effective application of pulsed power. The higher powerful and technological advantages for purification of wool from vegetable impurities are presented in this paper. The aim of using light irradiation is almost complete cleaning of light wool from dark vegetable admixtures, dust and brand at the early steps (carding worsted blends) of technological process of producing fine yarns. Stabilizing all mechanical and chemical-technological processes following light radiation purification and increasing technical-economic parameters of production is achieved in this case as well. The physical essence of light irradiation wool cleaning is based upon different optical and thermal properties of light fibers on the one hand, and of dark admixtures-fractions of vegetable matter and burrs, dust and brand-on the other hand. The difference of coefficients of light irradiation by fibers and impurities is of great importance. The 500-1100 nm spectral range has a selective impact on the fibers and impurities.

Substantial progress in power scaling of diode-pumped monolithic Nd:YAG ring lasers is reported. By using a new crystal geometry with a negative curved front facet the thermally induced lens inside the active medium is partially compensated. Applying this design single-frequency operation at 1064 nm is observed at output powers of more than 1.8 W cw. Coherent superposition of the radiation from two miniature ring lasers is achieved by injection locking of these systems. Amplitude and frequency stability of the miniature ring lasers will be discussed for the free-running and the injection-locked laser systems.

A longitudinal multimode model based on rate equations has been developed for the simulation of Er doped LiNbO₃ waveguide lasers in dynamical regime. The model takes into account the time evolution of the population inversion, the transversal and longitudinal saturation effects due to signal and pump power, the dopant and field profile and the spatial hole burning in transversal waveguide section. The model has been applied for Q-switching simulations. Results about pulse peak power and width, spectral width and signal evolution with different coupled pump power and loss modulation frequency are reported.

Scatter in data of bandwidths is investigated both theoretically and experimentally. The model of Stokes wave with statistical character of phase jumps originating in quantum fluctuations of vacuum field/polarization is offered. A good agreement between experimental result and theoretical curves is obtained.

We report the operation of an optical parametric oscillator (OPO) utilizing either potassium titanyl phosphate (KTP) or potassium titanyl arsenate (KTA) in a noncritically phase matched condition with the constraint of operation within a compact and ruggedized laser system. The design of a ruggedized OPO laser system presented some unique design requirements and are discussed. The discussions here deal solely with a fixed wavelength device. A comparison between KTP and KTA is given with regard to overall conversion efficiency and operational wavelength. Nominally identical crystals (size and surface coatings) of either material were utilized within the same resonator to give comparative data. We also report damage threshold values of KTP when used within an optical parametric oscillator. This data shows that the damage onset in these crystals is dependent on the parametric oscillation, and is not solely a function of the pump beam irradiance.

An analytical solution to the nonlinear time-dependent coupled wave equations describing a doubly-resonant degenerate optical parametric oscillator (DROPO) with arbitrary cavity mirror reflectivities and arbitrary nonlinear interaction strength has been obtained. This solution makes it possible to investigate the spatio-temporal behavior of the optical fields in the cavity when the DROPO is pumped by a source having any desired temporal intensity profile for any values of cavity mirror reflectivity. The influence of pumping source parameters such as pulse duration and peak pulse intensity on the behavior of the DROPO is studied for different mirror reflectivities, as are the effects of absorption and cavity length. The predictions of the theory are compared to some existing experimental data.

The way of the general dot tracking is not suitable for the near distance laser radar tracking and neither is the imaging tracking because of the lower imaging rate. A new tracking method which is called as the Staring Target Edge Tracking (STET) is therefore discussed in this paper. The physical model and range equation of the STET are presented, and the demands to the optical system are analyzed. This method provides a new analyzing way for miniature laser radar.

The design of two-component unequal layer thicknesses multilayer dielectric coatings and the relationship between their spectral response characteristic and optical thicknesses and refractive indices of the layers are discussed. A solution of the problem of suppressing the high reflection zones at any harmonic frequency is proposed. The results of synthesis of the antireflection coatings for some widely separated wavelengths are discussed.

It is shown that the main processes limiting the output energy of powerful YAG:Nd lasers consisted of a master oscillator and multipass amplifier with a phase conjugation mirror via stimulated Brillouin scattering (SBS) are, first, the amplifier self-excitation involving spontaneous Rayleigh scattering in SBS-liquid, and, second, the two-pass amplified spontaneous radiation propagating along active laser rods. Comparison of various optical schemes of the multipass amplifier shows that the maximal output energy of the two-pass amplifier is 3-4 times as high as that of the four-pass one owing to a higher threshold for those phenomena. Under optimal conditions the one-pass low-intensity gain is limited to a level 2 X 10⁴ divided by 3 X 10⁴, and the maximal energy density reaches approximately equals 3.75 J/cm² and is almost independent of the reflectivity of the SBS-mirror and the input energy density down to approximately equals 0.1 mJ/cm². It is shown that the self-excitation of the multipass amplifier can result in the spontaneous generation of powerful 15 divided by 30 ns pulses with inhomogeneous intensity cross-section distribution.

The construction peculiarities and output parameters of two YAG:Nd lasers of high quality output radiation using a two-pass amplifier with a phase conjugated mirror are discussed. The first one has the following parameters in each of two channels: pulse energy at 1064 nm - 1900 mJ, at 532 nm - 700 mJ, at 355 nm - 250 mJ, at 266 nm - 130 mJ; beam divergence 0.3 mrad; line width 0.01 cm^-1; pulse duration 8 ns; repetition rate 1-5 Hz. The output parameters of the second one whose construction is based on the single flash lamp surrounded by four laser rods (one of the master oscillator, three others of the amplifier) are; pulse energy at 1064 nm - 350 mJ, at 532 nm - 130 mJ, at 266 nm - 25 mJ; energy stability at 1064 nm - 1.5%, at 532 nm - 4.5%, at 266 nm - 9.0%; repetition rate 1.15 Hz.

A narrow band, tunable Cr:LiSAF laser oscillator using self injection- locking for line narrowing was developed. With two etalons and one prism in the master oscillator arm of the composite resonator, output energies of up to 75 mJ/pulse were obtained with a linewidth of 1.5 pm FWHM at 830 nm, and a pulsewidth of 70 ns. This linewidth was achieved without the use of a separate injection seed source. Up to 530 mJ output energy was obtained in long pulse, free-running mode. The laser was tuned from 800 nm to 960 nm. the Q-switched laser data was consistent with the performance predicted by our model.

The technique of Type I quadrature doubling has been used to generate 266 nm output from 532 nm input. Using a simple flashlamp pumped Nd:YAG laser doubled in KTP, the best conversion efficiency from the second harmonic to the fourth harmonic was 42% using two KDP crystals. With a second harmonic conversion efficiency of 60%, the total conversion efficiency from 1.064 micrometers to 266 nm was 25%. Output energies at 266 nm of up to 11.5 mJ in a nearly diffraction-limited beam, and 22 mJ in a multimode beam, were obtained, limited by the pump laser. The transient nonlinear absorption of 266 nm induced in the KDP crystals was measured in our samples, and the effect was accurately modelled to predict performance of a harmonic conversion system using improved nonlinear crystals.

Femtosecond optical parametric oscillators (OPO), synchronously pumped by Ti:Sapphire lasers, operating in the near infrared (IR) region are an important light source now under active development. We report the results of our Ti:Sapphire synchronously pumped noncritically phase matched femtosecond OPOs that are based upon several crystals from the KTP family. The newly developed nonlinear crystal niobium doped KTP (Nb:KTP) has a greater birefringence than undoped KTP and is shown to extend the wavelength farther into the mid-IR. We report the first operation of a femtosecond OPO utilizing the solid-solution grown crystal Nb:KTP. Additionally, we show that CTA is very useful in mid-IR angle tuned OPOs.

Far-infrared (FIR) transmission spectra have been measured for several nonlinear crystals. The results show that both GaP and ZnGeP₂ have a fairly narrow Restrahlen band. After the Mid-infrared (MIR) cut off at wavelengths near 12 micrometers, the crystals begin transmitting again at wavelengths of 100 micrometers. The transmissivity is highly dependent on the conductivity of the samples as free carrier absorption will deleteriously affect transmission. These results indicate that these crystals may be used for generation of FIR radiation using difference frequency generation (DFG) from the Near-Infrared (NIR) or MIR. High resistivity GaAs and GaSe should have similar properties, but no high resistivity material was found. Other crystals such as LiNbO₃, LiIO₃, BBO and KTP may be used at longer wavelengths.

We report optical second harmonic generation measurements in single crystal (alpha) -SiC of polytype 6H. The sample was found to be optically uniaxial, consistent with the hexagonal symmetry of the crystal structure. The two independent components of the second order electric susceptibility tensor were determined to be d₃₃ equals 43 pm/V and d₃₁ equals -4.3 pm/V. From this data the principle electro-optic coefficient was computed to be r₃₃ equals 100 pm/V. The corresponding figures of merit for nonlinear optical device operation compare favorably with leading materials such as lithium niobate and KTP, and thus the relatively convenient and inexpensive fabrication of 6H SiC thin films could prove useful for integrated optical devices.