We show by computer simulation that high beam quality can be achieved in high energy, nanosecond optical parametric oscillators by using image-rotating resonators. Lateral walk off between the signal and idler beams in the nonlinear crystal creates correlations across the beams in the walk off direction, or equivalently, a restricted acceptance angle. This tends to improve beam quality in the walk off plane. We show that image rotation or reflection can be used to improve beam quality in both planes. The lateral walk off can be due to birefringent walk off in type II mixing or due to noncolinear mixing in type I or type II mixing.

Periodically-poled lithium niobate (PPLN) has been used to convert the 1.064 micrometer emission from a diode-pumped Nd:YAG laser to give an emission close to 4 micrometer. An acousto-optical Q-switch was used for generating short- duration, high-intensity pulses. Modulated waveforms are possible via direct modulation of the diode sources. A simple OPO configuration has been used with a resonated signal beam passing through a PPLN crystal in an oven. The pump beam has good beam quality, having an M² of about 1.8 in each axis, and modulated average power in excess of 6 W. Damage has been observed to the output face of PPLN crystals over a range of pumping conditions and OPO configurations. The estimated damage threshold has been surprisingly low, of the order of 1.5 J/cm². First observations indicated the damage occurring consistently at the output face of the crystal, but further analysis has indicated the presence of bulk damage, typically starting at domain boundaries.

The construction of a double, synchronously pumped OPO is described. It generates pulses with duration 25 ps and repetition rate of 10 Hz. The bandwidth of the radiation is 1.36 cm^-1, close to the Fourier limit. A single pulse from each oscillator is further amplified with an OPA obtaining pulse energies up to 3.7 mJ. This source can be tuned between 410 nm and 2000 nm.

Use of photons for in-situ measurements of various objects provides a number of benefits, such as precise real-time measurement with no effect on the measured objects. Our research aims to develop an in-situ measurement technology that uses the benefits of photons and is ideal for applications in production lines. We succeeded in developing a tunable laser beam source to obtain the spectral line width of 5 MHz and a continuous wavelength sweep bandwidth of 200 nm, thus achieving our initial target. We believe that these characteristics are sufficient for use in absorption spectroscopy measurement of gases. For a 2.5 - 2.7 micrometer- band quantum infrared photo detector, we achieved the initial target of D* equals 1 to 3 X 10¹¹ cmHz^1/2/W (at room temperature). For a 3 - 10 micrometer-band quantum infrared photo detector, we performed a study on designing an InAsP/InP multi-quantum well light-absorbing layer.

We introduce the theory of intracavity quasi-phase-matched three-frequency wave interactions in active-nonlinear periodically poled medium, and in particular, self-frequency doubling and halving. The combination of laser oscillation of active ions with nonlinear optical properties of the host material provides an opportunity for creation laser with self- frequency conversion. Quasi-phase-matched second harmonic generation at 0.542 micrometer by self-frequency doubling of fundamental radiation laser radiation at 1.084 micrometer in periodically poled Nd:Mg:LiNbO₃ crystal pumping by diode laser at 0.810 micrometer has been observed experimentally.

In this paper we report on the design and performance of the large KDP crystal plates that were constructed to convert 1.054 micrometer laser beam to its third harmonic. The KDP crystals were AR-coated by sol-gel films. Type II/type II phase-matching configurations for cascade frequency doubling and tripling have been implemented at 250 mm aperture. High conversion efficiencies approaching to 70% were achieved. Focusing properties of harmonic beam are also investigated in the paper. Based on the transfer of electric-field amplitude and phase ripple in frequency tripling, simple formulas are derived for the harmonic laser beam-quality factor, M_3(omega )², with an arbitrary fundamental beam incident to ideal nonlinear crystals. Harmonic beam-quality is generally degraded, while the beam divergence is similar to that of the fundamental after a nonlinear frequency-conversion process. For practical crystals with periodic surface ripples due to their machining, a multi-order diffractive model is presented to study the focusing properties of harmonic beam. Predictions of the theories are shown to be in excellent agreement with full numerical simulations of tripling.

An area of CsLiB₆O₁₀ (CLBO) phase equilibrium in the (Cs₂O-Li₂O) -- B₂O₃ -- MoO₃ system was determined with spontaneous crystallization method. Crystals of 75 X 60 X 40 mm³ size have been growth in [100] direction with Kiropulos method. The forth-harmonic generation (270 nm) was achieved through the doubling of second-harmonic frequency in a multi-mode Nd:YAP laser in the type 1 collinear phase-matched geometry. The second-harmonic radiation in the technological laser of 3 mrad divergence was focused onto the input face of the crystal by a long-focus quartz lens. The input power density of the second harmonic was 300 MW/cm². Using a 11.5 mm crystal, we showed that the highest efficiency of the forth-harmonic generation is 30%. The fifth harmonic (216 nm) in CLBO crystal was generated by composing the main laser beam and the forth-harmonic beam under the type 1 collinear phase-matching. Both beams were converged with dichroic and turning mirrors and then focused by a long-focus quartz lens. Our experiments showed that the fifth-harmonic generation in a multi-mode technological laser of 3 mrad divergence is possible in a 10 mm CLBO crystal of 23% optical conversion efficiency. The input power density of the forth harmonic was 100 MW/cm². The use of longer CLBO crystal is less effective due to the nonlinear UV absorption and the walk off between the pump beam (1079 nm) and the harmonic beam.

The optical properties of LiInS₂ suggested it as a promising material for generation of coherent radiation in the mid-IR region. Before investigating such capabilities its optical and mechanical properties have to be characterized precisely, and especially their evolution with temperature. Sufficiently large and suitably oriented crystals of good optical quality were studied. We first deduced the transparency range of these samples, as well as the frequencies of the optical phonons. We observed a phase- matched second-harmonic generation, using a nanosecond-OPO in the range 2.4 - 2.6 microns as the pump source and estimated a first value of the type-II nonlinearity d_eff(XY) equals 7.4 pm/V. The thermal expansion, thermo-optic, piezoelectric and electro-optic coefficients were determined along the three principal directions of polarization from -20 degrees Celsius up to + 120 degrees Celsius by means of original interferometric methods. A so-called Fabry-Perot Thermal Scanning (FPTS) interferometric method has been developed to measure accurately the electro-optic coefficients. For LiInS₂ the values of r_i3 were found to be of the same order of magnitude as its piezoelectric coefficients, but around one order of magnitude smaller than the electro-optic coefficients of the well known KTiOPO₄.

We propose new smoothing techniques involving nonlinear cascaded processes. The scheme is based on the transfer of incoherent amplitude modulations of a pump beam to the phase of a monochromatic plane wave signal. For that, we can use nonlinear cascaded processes which create crossed phase modulation without efficient energy transfer. With this technique, we should be able to produce a temporal or/and spatial incoherent phase modulation without using electro- optic devices. We describe the mechanisms and the different schemes we propose such as a random temporal phase modulator or a temporally varying random phase plate. We present theoretical results by developing analytical calculations of the nonlinear phase. Then, we analyze the incoherent phase modulation with the correlation functions formalism. We present results which take into account temporal limitations such as the Group Velocity Dispersion (GVD) or the Group Velocity Walk-off (GVW) and spatial limitations such as the Diffraction and the Spatial Walk-off. Finally, we present an all-optical sinusoidal phase modulator setup.

Non linear optical response and reverse saturable absorption behavior of various rare earth phthalocyanines such as Nd, Eu, Sm and La in di-methyl formamide (DMF) solution were studied under high power Nd:YAG laser excitation. The size of the central metal atom of the Pc ring is found to considerably affect the nonlinear response of these systems. Excited state absorption cross sections of these systems are measured from the limiting characteristics. The SmHPc₂ system yields maximum value for absorption cross-section and its potential application in DMF as a suitable optical limiter is also discussed.

A super-resolution near-field structure (super-RENS) has an additional mask layer in the usual phase change optical disk. A thin layer of antimony (Sb) film or a silver oxide (AgOx) layer is used as a mask layer. By focusing a laser beam, a transparent aperture in the Sb layer and a light scattering center in the AgOx layer are formed transitionally, whose diameters are smaller than that of the laser beam spot. The changed portion can generate an intense optical near field and can be used to record and retrieve small marks beyond the diffraction limit. The nonlinear optical properties of Sb and AgOx films with protective layers were examined using a pulse laser. Optical switching, their time response and transient spectroscopic change were investigated. Light scattering property of AgOx film was also examined. A repeated optical switching action can only be realized if the illuminating spot size is confined to very small areas. Time response of Sb film shows first rise-up and then slow exponential decay. Time response of AgOx film shows more complicated decay than Sb film. Transmittance spectra just after the pump irradiation becomes flat over wide spectral range both in Sb and AgOx layers. Scattered light is extremely enhanced by increasing the input light power.

This paper reports investigation on third-order nonlinear optical properties of chlorophyll a (Chl a), a kind of natural porphyrin derivative in organisms, by using Z-scan streak- camera system on nanosecond and picosecond time scale. Time- dependant behavior of the third-order optical nonlinearity was examined within duration of a picosecond pulse train along Z direction, and modulation of the transmitted pulses in the pulse train was temporally observed. A slow-accumulated optical nonlinearity was occurred in the diluted Chl a solution besides fast response optical nonlinearity of electronic origin. We propose that the slow-accumulated optical nonlinearity is originated from pileup of triplet states, and that the triplet states accumulation is attributed to enhancement of singlet-triplet orbit coupling brought about by intense optical field of the laser pulse.

Using Raman fiber laser (RFL), 350 m singlemode fiber and 50% feedback fiber Bragg grating (FBG) at 1484 nm, we obtain a high-efficiency ultra-broadband (1434 - 1527 nm) CW Supercontinuum (SC) centered at 1484 nm with an average output power of 2.08 W and nonlinear conversion efficiency of 94%. Spectral density of 22.3 mW/nm is obtained. The output of the SC for different fiber lengths in the Raman and the singlemode are reported.

BaWO₄ and KGd(WO₄)₂ (KGW) tungstate crystals (33 mm and 40 mm of length, respectively) were investigated as Raman frequency converters of picosecond and nanosecond second-harmonic Nd:YAG pulses. During the experiment the threshold energy of stimulated Raman (SR) process, generated wavelengths, and energy for nanosecond and picosecond pump pulses with both nonlinear crystals were measured. For BaWO₄ crystal, the threshold pumping intensity was measured to be 530 MW/cm² for psec pumping and 200 MW/cm² for nsec temporal region. The corresponding Raman gain values were 14.3 cm/GW (picosecond pump) and 38 cm/GW (nanosecond gain). For KGW crystal the threshold intensity values 530 MW/cm² for psec and 340 MW/cm² for nsec were measured with corresponding Raman gain values of 11.8 cm/GW (psec) and 18.6 cm/GW (nsec). The Stokes components up to the third order in both psec and nsec regions were detected. Temporal length measurements of pump and Stokes pulses in both crystals revealed pulse shortening by a factor of approximately 2 during the SR process. Due to a high value of Raman gain of a new BaWO₄ crystal under both nsec and psec pumping, this crystal can be considered as a unique candidate for utilization in solid-state Raman laser systems.

We present a new, to our knowledge, method of anti-Stokes generation at stimulated Raman scattering in media with variations of third order nonlinearity ((chi) ⁽³)) along longitudinal coordinate. By numerical simulation the quasi- phase matching condition in different media and achievement of high efficiency of anti-Stokes conversion are obtained. The dependence of energy conversion from pump into anti-Stokes wave on the relation of input intensity of pump and Stokes waves is computed. We received the models of media in which the efficiency of anti-Stokes generation exceeded 30%. The results of the study can be used for the development of new effective nonlinear-optical devices for laser frequency conversion.

The temporal compression with amplification and generation of powerful femtosecond pulses using stimulated Raman scattering in gases is studied by numerical simulation. Optimal values of medium parameters (Raman gain coefficient, group velocities dispersion) for highest conversion efficiency are determined. The dependence of Stokes wave amplification on input pulse duration and intensity is analyzed. The results can be used for development of effective nonlinear conversion devices of ultrashort laser pulses.

We describe a technique for the simultaneous measurement of all the modal birefringences in a (chi) ⁽²) optical guide through surface emitting second harmonic generation (SESHG), which we applied to multilayer AlGaAs waveguides at 1319 nm, both before and after selective AlAs oxidation. By end-fire coupling linearly-polarized laser pulses into ridge waveguides, both forward- and back-propagating eigenpolarizations were excited due to Fresnel reflection at the output facet. Several TE-TM pairs of counterpropagating modes then interact through the quadratic nonlinearity, giving rise to interference of SESHG fields. With a single image acquisition of the SESHG far field by a CCD camera, we could evaluate the modal birefringences between all the excited TE- TM mode pairs at the fundamental frequency. This simple approach led us to estimate form-birefringence of our multilayer quadratic waveguides with the high accuracy required by optimized phase-matched interactions in parametric generators and oscillators. This technique is a valuable complement to standard m-line effective index evaluation, and a versatile one-shot tool for waveguide diagnostics.

Nowadays refractive-index engineering has become a challenging area for experimentalists in semiconductor integrated optics, whereas design constraints are often more strict than both standard technology tolerances and model accuracies. In fact, it is crucial to non-destructively evaluate thicknesses and refractive indices of a multilayer waveguide independently, and to this aim we resorted to X-ray reflectometry and effective index measurements on MBE-grown AlGaAs waveguides, respectively. With the first technique interference effects (Kiessig fringes) arise, which are related to layer thicknesses. By standard data processing, thickness accuracies of +/- 0.05 nm are readily achieved. Effective index measurements were performed at several wavelengths on both slab and rib waveguides, through grating-assisted distributed coupling with both photoresist and etched gratings. Effective indices were determined with an absolute precision as good as 1/2000, adequate for phase matching in parametric devices. Merging thickness and effective index evaluations, the refractive indices of the constituent layers were determined with unprecedented accuracies, in substantial agreement with existing models.

We numerically investigate efficient frequency doubling of near infrared light in a coupled system of buried and surface waveguides obtained by Reverse Proton Exchange in z-cut Lithium Niobate. For a monomode TE surface guide at 1.32 micrometer and a highly multimode TM (buried) guide at 666 nm and exploiting the d₃₁ nonlinear tensor element, for planar structures we calculated conversion efficiencies as high as 14% micrometer/W cm, with a weak dependence on temperature. Noticeably, this geometry features the physical separation of the harmonics at the output.

As the demand for optical fiber communications bandwidth grows, the implementation of signal processing functions using all-optical techniques becomes increasingly attractive. In recent years, a number of methods have been used to perform functions such as wavelength conversion for WDM systems, gated mixing for TDM multiplexing and demultiplexing, spectral inversion for dispersion compensation, and all-optical switching. Three-wave mixing in (chi) ⁽²) media is an attractive approach, presenting a combination of low pump power, wide bandwidth, and negligible degradation of signal to noise ratio. In this paper, we describe optical frequency mixers implemented using annealed proton exchanged waveguides in periodically poled lithium niobate. These devices have been used in a variety of system experiments. We present several WDM demonstrations, including wavelength conversion, dispersion compensation by mid-span spectral inversion, and compensation of Kerr nonlinearities. We also discuss TDM demonstrations such as efficient all-optical gating and multiplexing/demultiplexing of high bit-rate data streams.

Several Tm,Ho-doped LuLF and YLF crystals were grown using the Czochralski method. Crystals were pulled in a furnace with atmospheric control system. Pulling and rotation rates were 1 mm/hr and 15 rpm, respectively. High purity (>= 99.99%) fluorides were used as starting materials. High vacuum (approximately equals 10^-5 torr) prior to the growth and CF₄ gas during the growth were applied. Single crystals of up to 20 mm in diameter and 80 mm in length were successfully grown. Various laser rods of sizes 4 X 3 X 2.7 mm³ were prepared from the grown crystal boules. The crystal ends were Brewster- cut to minimize the reflection losses inside the cavity. Two quasi-CW LD-arrays of 6 X 60 W each side-pump the crystals. The pump beam is focused using two lens ducts of length 64 mm to a waist of 2.5 X 2.5 mm². The nearly hemispherical laser cavity is formed by a flat high reflector and a 300 mm radius of curvature 5% transmission output coupler. At room temperature, up to 13.5 mJ (9.9 mJ) with a slope efficiency of 10.5% (7.5%) has been demonstrated at 1 Hz for 5% Tm, 0.5% Ho:LuLF (5% Tm, 0.5% Ho:YLF).

BBO crystals ((beta) -BaB₂O₄) exhibit unique nonlinear- and electro-optical properties, which provide their wide application in laser techniques. The growth of BBO is a technologically sophisticated procedure enabling the production of big high-quality single crystals. The growth of BBO crystals is performed with high-temperature melt-solution crystallization method, most commonly in the BaO-B₂O₃- Na₂O ternary system. The typical effect of constitutional supercooling results from a high viscosity of the melt- solution and the fact that a growing BBO crystal shields the crystallizing melt, thus removing heat away from crystallization interface. The contribution considers the possibility of the improvement of crystal growth process via the change of heat field symmetry and its rotation. The symmetry of a static heat field reducing from L_{varies direct as} to L₃ results in stronger convection and, therefore, larger crystal. On the other side the permanent symmetry of a heat field -- static or rotating -- commonly provokes the formation of a quite big defect area in the central part of a grown boule with the signs of cell growth. To improve the convection in the central sub-crystal area we performed the BBO crystal growth process in a rotating heat field, which is free of the symmetry axis coinciding with the symmetry axis of the growth furnace/crucible. The experiments showed that the crystal with a defect-free central area can be successfully produced.

Ce-doped LiCAF (Ce:LiCAF), LiSrAlF₆ (Ce:LiSAF) and LiSr_0.8Ca_0.2AlF₆ (Ce:LiSCAF) single crystals were grown by the Czochralski technique as ultraviolet, tunable, solid- state laser media. Optical characterization and Laser activity were investigated. Crystal growth was performed in Czochralski system (CZ) under an atmosphere of CF₄ with previous treatment in high vacuum (approximately equals 10^-2 Pa). Under such conditions, we succeeded to grow Ce:LiCAF, Ce:LiSAF and Ce:LiSCAlF (18 mm in diameter and 60 mm in length) single crystals. Laser rods were cut from the above mentioned crystal boules. The laser resonator was established by a flat high reflector and a flat output coupler. The forth harmonic of a Q-switched Nd:YAG laser was used as the pumping source. Laser oscillations at around 290 nm were measured. 60 mJ pulses were generated directly from the Ce:LiCAF crystal. Gain has been observed for the Ce:LiSCAlF crystal and laser oscillation was confirmed.

Single crystals of the noncentrosymmetric barium borate, Ba₂B₁₀O₁₇, have been grown by slowly cooling a stoichiometric melt.The material crystallizes in the triclinic space group P1 with cell parameters a equals 9.858(1), b equals 9.990(1), c equals 6.706(1) angstrom, (alpha) equals 96.79(1), (beta) equals 106.64(1), and (gamma) equals 76.89(1) degree(s). The structure is a new type characterized by a condensation of B₃O₈ rings and BO₃ triangles. A calculation of the second-order nonlinear susceptibility coefficients on the basis of the orientations of the tetrahedral and triangular borate groups in the rings and triangles has yielded a maximum coefficient of d₁₁ equals 0.2 pm/V. This result is consistent with the measured second- harmonic signal -- 0.5*KDP. Partial solid solubility of Sr in the host -- Ba_2-xSr_xB₁₀O₁₇ (0 < X