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Optical channel waveguides in Nd/Ce codoped YAG laser crystal have been fabricated by using mask-assisted carbon ion implantation. The measured waveguide mode distributions were in good agreement with the calculated modal profiles, which implies the feasibility of designable devices. After thermal annealing treatment at 260[degrees]C for 30 min in air, the propagation loss of the waveguide was reduced down to ~2 dB/cm at a wavelength of 632.8 nm. The microluminescence spectra of the waveguides show that the fluorescence properties of both Ce and Nd ions (including the energy transfer between them) are not significantly affected by the waveguide formation processing, which indicates a fairly good potential for further laser actions in a compact device. OCIS codes: 230.7380, 130.3120, 160.3380.

Bulk laser-induced damage at 1064 nm has been investigated in KTiOP[O.sub.4] (KTP) and RbTiOP[O.sub.4] (RTP) crystals with a nanosecond pulsed Nd:YAG laser. Both crystals belong to the same family. Throughout this study, their comparison shows a very similar laser-damage behavior. The evolution of the damage resistance under a high number of shots per site (10,000 shots) reveals a fatigue effect of KTP and RTP crystals. In addition, S-on-1 damage probability curves have been measured in both crystals for all combinations of polarization and propagation direction aligned with the principal axes of the crystals. The results show an influence of the polarization on the laser-induced damage threshold (LIDT), with a significantly higher threshold along the z axis, whereas no effect of the propagation direction has been observed. This LIDT anisotropy is discussed with regard to the crystallographic structure. OCIS codes: 140.3330, 260.1180, 160.4330, 160.2100.

We report on frequency measurements of a free-running Nd:YAG laser operating at temperatures down to 6.5 K using a femtosecond laser frequency comb. Due to lower thermal expansion and thermo-optic effects as well as reduced electron-phonon interactions in Nd:YAG at cryogenic temperatures, a laser frequency stability on the order of [10.sup.-11] at [tau] [less than or equal to] 30 s has been achieved. Within a one-week measurement period, absolute frequency deviations were lower than 1.85 MHz. This is up to a 100-fold improvement of frequency stability compared to any existing free-running solid-state laser. OCIS codes: 120.3940, 140.3530.

An undoped YVO4 crystal is employed to achieve efficient stimulated Raman scattering conversion in a diode-pumped actively Q-switched Nd:YAG laser. With an incident pump power of 16.2 W, an 1176 nm first Stokes average output power of 3.0 W was generated at a pulse repetition rate of 50 kHz, corresponding to an optical-to-optical conversion efficiency of 18.3%. Moreover, the maximum optical-to-optical conversion efficiency of 21.3% was found at 20 kHz. The maximum pulse energy is higher than 83 [micro]J at both 20 and 30kHz. With an incident pump power of 7.6W, the underestimated peak power of 43.5 kW was demonstrated at 20 kHz with mode-locked modulation. OCIS codes: 140.3480, 140.3540, 140.3550, 290.5910.

This paper presents a new low-noise high-accuracy laser range finder based on the Time-Of-Flight (TOF) method. A Q-switched Nd: YAG laser at 1064 nm as a source and a SLIK avalanche photodiode as a detector are used. The optical section of the system including ZnS/Mg[F.sub.2] optical filter, designed by [C.sup.++] and Zemax software, has been successfully implemented and tested. The quality factor of the optical filter is obtained about 2.53. Using the 1.5 MW Nd: YAG laser, the lowest detectable optical power is limited to about 8.14 nW. The absolute range finding error in the range of 0.3-20 km is also measured as [[delta].sub.r] = [+ or -] 50 cm. Furthermore, the sampling rate of the distance measurement can be adjusted between 1 and 20 samples per second. Keywords: Time-of-flight, laser range finder, Q-switched Nd: YAG laser, optical filters, INTRODUCTION Time-of-flight method is the most widely used technique for long distance measurement over length scales of several hundred meters to tens of kilometers. Continuous wave lasers are usually being [...]

The unique ablation characteristics of gold nanoparticle film on polymer obtained by using frequency doubled Nd:YAG (YAG = yttrium aluminum garnet) nanosecond laser are presented. The film could find application in ink-jet printed electrical microconductor.

A diode-side-pumped high-power 1319 nm single-wavelength Nd:YAG continuous wave (cw) laser is described. Through reasonable coating design of the cavity mirrors, the 1064 nm strongest line as well as the 1338 nm one have been successfully suppressed. The laser output powers corresponding to four groups of different output couplers operating at 1319 nm single wavelength have been compared. The output coupler with the transmission T = 5.3% has the highest output power, and a 131 W cw output power was achieved at the pumping power of 555 W. The optical--optical conversion efficiency is 23.6%, and the slope efficiency is 46%. The output power is higher than the total output power of the dual-wavelength laser operating at 1319 nm and 1338 nm in the experiment. OCIS code: 140.3480.

A laser's delivery of constant beam parameters with good quality, independent of the pump power using self-adaptive overcompensation is demonstrated. With this technique, the brightness of a Nd: YAG laser increased by almost an order of magnitude despite highly aberrated thermal lens in the laser rod.

Simultaneous oscillation at 1060 and 1090 nm is demonstrated from a diode-cladding-pumped Nd[subscript 3+]-doped multicomponent silica glass fiber laser is demonstrated and discussed.

Glasses, fluids, and gels for the thermooptical compensation of thermally induced distortions in high-power laser resonators (LR) are examined. Designs for the compensation element are also discussed.

The objective of this study is to investigate experimentally the mixing of transversely injected jets into a crossflow under low-density conditions. This study has application in nitrogen-diluted subsonic chemical oxygen iodine lasers. The investigation was performed nonintrusively, using planar-laser-induced fluorescence. A frequency doubled Nd:YAG laser was used as the excitation source, and the iodine fluorescence was imaged using a charge-coupled device camera. Experiments were performed for a variety of crossflow velocities and injection pressures. A parameter, degree of unmixedness, which was defined using variance of the image intensities, was used to quantify the mixing. Mixing distance was defined as the location downstream of which the degree of unmixedness did not exceed 0.05. The mixing distances obtained were correlated using the ratio between the momentum flow rates of the injected jets and the crossflow. The mixing distances were linearly dependent on this ratio until a value more than which the jets mixed almost at the injection location. This linearity depended on the injection configuration. The correlation was found to be a weak function of the injector hole diameter. Diffusion is the main mixing mechanism in this low-Reynolds-number flow regime, and thus the spatial distribution of the injector holes in the array played an important role in mixing.

We fabricated and analyzed the output power and polarization characteristics of an efficient diode-side-pumped Nd:YAG rod laser with a diffusive optical cavity. The resonator stability conditions are analyzed graphically in the symmetric and asymmetric configurations for a plane-parallel resonator. On the basis of an analysis of the stability condition and mode size for the r and [theta] polarizations, we clarify how the stable laser operation is possible for various resonator configurations. In particular, we show that the critical stability region of around [g.sub.1.sup.*] [g.sub.2.sup.*] = 0 provides a stable resonator in the symmetric resonator, even with a slight asymmetry. Experimentally, the output power and polarization characteristics are confirmed in association with the resonator stability condition. OCIS codes: 140.3410, 140.3480, 140.3530.

A passively Q-switched quasi-three-level Nd:YAG laser is intracavity frequency doubled to generate a blue laser. The 473-nm blue laser has a peak power of 37 W and a pulse width of 23 ns at a pumping power of 1.6 W. To model this laser numerically, we developed rate equations by taking into consideration both the quasi-three-level nature of the gain medium and the four-level nature of the saturable absorber. Good agreement was achieved between experimental and simulated results for both the fundamental and the second-harmonic output. The reabsorption loss of the gain medium is estimated under pulsed operation. OCIS codes: 140.3540, 140.3480, 190.2620, 190.5940.

Research is presented concerning the experimental and numerical investigation of a Nd: YAG laser to determine the role of various sources of noise at the initial stage of the formation of the nonlinear cavity.

Research is presented concerning the development of a formalism for passively Q-switched laser system analysis. The analysis of system optimizations and sensitivity studies is discussed.

Research is presented concerning the use of a single-frequency lower-power stable master laser in the injection-locking of a slave laser as a technique for the production of a single-frequency higher-power stable laser.

Research describing laser drilling of alumina and silicon nitride ceramics is presented. In particular the work is based on the heat transfer equation of a one dimensional model.

Research describing passively Q-switched neodymium lasers is presented. In particular the relative performance of Nd:YAG, Nd:YALO and Nd:BEL at 1.3um for Co:ZnS saturable absorbers is investigated.

The spectroscopic and laser properties of neodymium-doped yttrium aluminium borate are examined.

Simultaneous multiple-wavelength cw laser operations were achieved in two types of composite laser rod composed of [Nd.sup.3+]:YAG and [Nd.sup.3+]:YLF crystals, which were laser diode (LD) pumped within a single virtual-point-source cavity. As much as 30 W of total output at 1064- and 1047-nm wavelengths was obtained under 150-W LD input power, with approximately 25% from the 1047-nm wavelength. Different bonding methods were compared, showing that the use of an optical adhesive is effective and presents no deterioration at low and middle power levels. Simultaneous multiple-wavelength operation at 1064- and 1053-nm wavelengths was also studied.

Unidirectional single-mode operation of a diode-pumped Nd:YAG laser with a planar semimonolithic ring cavity has been demonstrated at 1064 nm. The semimonolithic cavity consists of a laser active medium placed in a magnetic field, a crystal quartz plate, and an output coupling mirror, which form an optical diode by acting as a Faraday rotator, a reciprocal polarization rotator, and a partial polarizer, respectively. A single-mode output power of 155 mW and a slope efficiency of 17% were obtained with a 1.2-W diode laser at 809 nm. A laser linewidth of less than 100 kHz is inferred from a beat note frequency spectrum between two identical laser systems and continuous tuning to greater than 2 GHz was observed.

A laser-diode-pumped high-repetition-rate zigzag slab Nd:YAG oscillator-amplifier system is developed as the pumping source of a high-average-power and terawatt Ti:sapphire chirped pulse amplification laser system. This system can produce a greater than 2-J high-energy fundamental laser pulse at a repetition rate of 100 Hz. The frequency-doubled energy with a diffusion-bonded KTP crystal is 1 J at a repetition rate of 100 Hz.

We fabricated a compact diode side-pumped Nd:YAG laser with a diffusive reflector, in which the diode laser power is transferred directly into the threefold symmetric diffusive cavity through long narrow slits. With a 7.5% output coupler in a linear resonator, we obtained 62.4-W multimode output power with an optical slope efficiency of 53.4% at a diode power of 182 W, which corresponds to an optical-to-optical efficiency of 34.3%. The optical slope efficiency increased to 55.5% when we used an 11% output coupler. From the leakage power analysis method, the pumping efficiency was measured to be approximately 82%. We discuss the thermal lens and the slope efficiency with respect to absorbed power that is derived from the measured pumping efficiency.

We present experimental results that demonstrate the great efficiency of a core-doped Nd:YAG rod (a hexagonal Nd:YAG core surrounded by undoped YAG) in producing high output power and excellent beam quality. An additional improvement in beam quality is dearly observed when the core-doped rod is used in combination with a LiF:[F.sub.[2.sup.-]] crystal, which acts as a passive Q-switching element. This improvement is quantified by beam-propagation factors as low as [M.sup.2] [approximately equal to] 4 at a maximum average output power of 9 W. We show that transversally pumped core-doped rods with the addition of LiF:[F.sub.[2.sup.-]] crystals fulfill the requirements for high-beam-quality, scalable, compact all-solid-state lasers in passively Q-switched operation.

The stability of a high-power diode-side-pumped intracavity-frequency-doubled CW Nd:YAG laser was investigated. Findings showed that large green power fluctuations seen in experiments can be inhibited by compensating thermal lensing of the nonlinear crystal: KTP and that of the Nd:YAG rods with an advanced resonator design. Stable CW green powers of 27 W with a beam quality of M2 = 8 and 16 W with M2 = 1.2 were achieved.

A four-pass two-channel Nd:YAG laser having two amplifier rods in each channel was examined. Results showed that the laser configuration can compensate for aberrations and polarization distortions in Nd:YAG crystals of 15-mm diameter at a repetition rate of 25 Hz and can combine two channels of radiation into a single diffraction-limited beam. The energy of the laser output beam was found to be more than 5 joules.

The amplified spontaneous emission was modeled to examine the differential equations describing the evolution and decay of the upper laser manifold population density. Results from the measurement of the gain as function of time and pump energy agree well with the model. Based on the results, a flashlamp-pumped Nd-YAG laser was developed to operate at 0.946 micron and was found to yield a threshold of 12 joules and a slope efficiency of 0.0009 at room temperature.

A rate equation model with spatial hole-burning effect was devised to compute the Q-switch Nd:YAlO3 simultaneous dual wavelength laser. Results showed that 1341.4 and 1079.5 nm lasers can be simultaneously obtained in a linear cavity by regulating the output coupling rates of the two coherent radiations. On the other hand, a Y cavity and devices to regulate relative Q-switch delay were needed for the dual wavelength Nd:YAG lasers in previous studies.

Mixtures of methane, hydrogen, and argon ([CH.sub.4]:[H.sub.2]:Ar) were studied as UV Raman shifters for ozone differential absorption lidar application. They have higher photochemical stability than pure [CH.sub.4] and the capability to produce, with high enough efficiency, either first [CH.sub.4] Stokes or, simultaneously, [CH.sub.4] and [H.sub.2] first Stokes with equal energies. These mixtures can be used as an inexpensive replacement for [D.sub.2] or a more stable substitute for pure [CH.sub.4] in single-pass high-power Raman shifters.

Periodically poled flux-grown KTiOP[O.sub.4] was used for efficient extracavity 1064-nm Nd:YAG laser frequency doubling. A conversion efficiency exceeding 65% was obtained in Q-switched operation, and 1.34 W of average frequency-doubled power was generated with 2.2 W of mode-locked laser output. The conversion efficiency is approximately two times higher for periodically poled KTP than for conventional type II phase-matched KTP. The measurements indicate that periodically poled KTP is less susceptible to optical damage than type II KTP.

Stokes pulses of high energy and high-average power were obtained by stimulated Brillouin scattering (SBS) compression of long Nd:YAG laser pulses. The SBS medium used in the single-cell compressor was liquid ultrafiltered Fluorinert FC-75 fluorocarbon. An output pulse duration of 0.9 ns and a peak-power enhancement by 1 order of magnitude were observed for 10-ns, 0.57-J input pulses at a 10-Hz repetition rate. The compressor internal SBS efficiency reached a value of [[Eta].sub.SBS] = 94% and the overall device efficiency a value of [[Eta].sub.dev] = 87%; both values are the highest reported so far to the best of our knowledge. The simple single-cell SBS geometry provided excellent energy and pointing stability of the Stokes pulse. Its temporal shape turned out to be somewhat less stable. The SBS process also partially improved the laser beam quality. The Stokes pulses proved to be capable of generating radiation in the extreme-ultraviolet and soft-x-ray regions over a period of two months without any significant output deterioration.

As much as 1.6-W average output power was emitted in a simple setup from a diffusion-bonded Nd:YAG rod with 70-100-ns Q-switched pulses at 946 nm and repetition frequencies between 15 and 45 kHz at 22-W incident diode-pump power. A [Cr.sup.4+]:YAG crystal with a bleachable loss of approximately 2.5% and a length of 0.5 mm was used as a saturable absorber. The extraction efficiency was 47% in comparison with the continuous-wave laser output power of 3.37 W in the free-running regime.

Excellent beam quality and divergence stability over a wide pump power range was demonstrated in a Q-switched, Nd:YAG, positive branch confocal unstable resonator by using a one degree-of-freedom, adaptive optic. Unlike single-element flexible-membrane mirrors, the variable radius mirror (VRM) consisted of a lens and mirror, whose separation determined the VRM's effective radius of curvature. This simple method enabled low cost and efficient thermal focusing compensation. The VRM was demonstrated by producing a 300-mJ Q-switch or 1-J free-running at a beam quality factor [M.sup.2] that varied between 1.2 and 1.8 as the average output power varied between 0 and 33 W.

Three different variants of a novel versatile Nd:YAG amplifier end pumped by fiber-coupled diode lasers were examined. The amplifier is very suitable to spaceborn applications due to its ruggedness, compactness and good efficiency. A numerical model was developed to simulate the gain and output power of the amplifiers. It was found to be in good agreement with the measured data and can be used to simulate the behavior of the amplifier by varying different parameters.

Research was conducted to examine beam scattering in laser welding. Several models for measuring the plasma plume properties including densities and the complex optical index were presented. Mie's theory was used to calculate the scattering parameters of the plume. Results based on the discrete ordinate technique agree with the spectroscopic measurements for small particle diameters.

Neodymium-doped benzil crystals have been synthesized and characterized for their absorption, emission, and kinetics properties. From Judd-Ofelt analysis, the radiative decay time of Nd emission (peaking at 1055 nm) is estimated to be equal to 441 [[micro]seconds]. The experimental Nd lifetime (under Ar+ laser excitation) is equal to 19 [[micro]seconds]. The broad emission band centered at approximately 700 nm ([[Tau].sub.decay] [approximately equal to] 15 ns) and the Raman scattering with characteristic frequency shift of 1600 [cm.sup.-1] have been observed at excitation of benzil with 532-nm Q-switched laser pulses. We show that rare-earth-doped benzil can be considered as a potential candidate for luminescent and solid-state laser material.

We present comparative studies on laser performance of diode end-pumped, composite Nd:YAG rods with undoped ends at 946 nm. Efficient heat removal in a composite rod can reduce the peak of rise in temperature in the active segment to 61% by theoretical calculation. The maximum, continuous-wave output power of 1.5 W, which is three times higher than a conventional noncomposite rod, was obtained at an absorbed pump power of 8 W because of the 55 deg reduction in temperature rise that was estimated experimentally. The performance and characteristics of composite rods in quasi-three-level laser operation are analyzed and discussed in detail, taking into account the reduction in reabsorption loss, which is strongly temperature dependent.

An extension to the 355- and 1064-nm wavelengths of a numerical optical model originally developed at 532 nm is presented. The resulting parameterization allows estimates of stratospheric aerosol surface area, volume, and extinction-to-backscatter ratio from lidar measurements obtained at one of the two Nd:YAG laser wavelengths. Functional relationships that link single-wavelength backscatter to each of the physical variables are provided for sulfate aerosol types ranging from background to heavy volcanic under environmental conditions representative of the global lower stratosphere. The behavior of the functional relationships at the three Nd:YAG wavelengths is compared. Relative errors of model estimates range between 10% and 50%, depending on wavelength and backscatter cross sections. These values are comparable with the ones that characterize in situ particle counters. The inference of particle effective radius and the application of the method to the interpretation of supercooled polar stratospheric cloud observations are discussed.

Lens ducts have the potential to couple the output from a laser diode array efficiently into the gain medium of a solid-state laser in an end-pumped configuration. Using a ray-tracing method we investigate different design approaches of lens ducts and demonstrate the possibility to obtain an output beam with a symmetric profile that is insensitive to the small displacement from the output surface of a lens duct.

We present what is to our knowledge the first theoretical and experimental estimation of the thermal characteristics of a composite Nd:YAG rod with an [Al.sub.2][O.sub.3] (sapphire) end in diode-end-pumped geometry. The peak temperature rise in the active segment is calculated to be reduced to 66% and the focal length of the thermal lens was measured to be reduced by 20% compared with a noncomposite Nd:YAG rod. By using a composite rod we successfully demonstrated the improvement of high-power performance that is due to reduction of thermally induced birefringence, which has not been observed in a composite rod with an undoped YAG end.

As far as we know this is the first report on picosecond green-light generation from an actively mode-locked diode-pumped self-doubling neodymium yttrium aluminum borate (NYAB) laser. The pulse width is approximately 100 ps and is limited by imperfect antireflection coating and the intracavity doubling effect. The green average output power of this laser for mode-locked operation was more than 12 tunes higher than that for the continuous wave NYAB laser. The polarization state of the laser can be switched from ordinary to extraordinary rays by displacement of the pump spot. The polarization ratio can be better than 200 without any intracavity polarization element.