This PDF file contains the front matter associated with SPIE Proceedings Volume 6455, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Design and experimental characterization of a nonlinear optical converter module for the generation of widely tunable UV radiation is presented. The module combines units for second, third and fourth harmonic generation of tunable Ti:Sapphire lasers. A modified conversion scheme based on the combination of BIBO and BBO crystals reduces the complexity of our former published UV setup - resulting in a significant increase of performance and long-term stability of the system. Experimental characterization of the former and the improved UV setup are compared. The investigations of the converter module are carried out with a widely tunable Ti:Sapphire laser with nanosecond pulses and a repetition rate of 1 kHz. This laser provides a continuous tuning range of 690 nm to 1010 nm with pulse energies up to 2.0 mJ and a spectral line width of less than 10 GHz resulting in an output power of the converter module of 1000 mW, 400 mW and 200 mW respectively for the second, third and fourth harmonic generation. The new converter module is a decisive step in the development of a hands-off solid-state laser system with a continuous tuning range from the UV to the NIR - 200 nm to 1000 nm.

We have constructed a blue laser source consisting of a single-frequency tapered diode laser with external cavity feedback that is frequency doubled by a quasi-phase matched KTP (PPKTP) in a bowtie ring cavity and extract more than 360 mW of power at 405 nm. The conversion efficiency from fundamental laser power to second harmonic power is 35 %, while it is 64 % from coupled fundamental power to extracted blue light. Thermal effects and gray tracking set an upper limit on the amount of generated blue light.

We present a novel ring resonator for second harmonic generation consisting of only two spherical mirrors and a refractive element. In our work we use periodically poled KTP as a nonlinear material for generating the second harmonic using an 808nm tapered grating stabilized external cavity laser as pump source. With 286mW of fundamental 808nm radiation coupled into the resonator, we generate 130mW blue light at 404 nm, resulting in a power conversion efficiency of 45%.

We have demonstrated single-pass frequency doubling of a ps Ti:sapphire laser with a periodically poled lithium niobate (PPLN) waveguide for spin polarization of ³He. Since the refractive index of PPLN varies with tuning the temperature, it is possible to control optimum fundamental wavelength for the second harmonic generation. We indicated that the tuning rate was about 0.06 nm/K. Moreover, we used the SHG light to conduct optogalvanic spectroscopy, which demonstrated that the linewidth of the SHG light could be incorporated in optical pumping transitions for the spin polarization

Mass spectrometry using matrix-assisted laser desorption/ionization (MALDI) technique is one of the most widely used method to analyze proteins in biological research fields. However, it is difficult to analyze insoluble proteins which have important roles in researches on disease mechanisms or in developments of drugs by using ultraviolet (UV) lasers which have commonly been used for MALDI. Recently, a significant improvement in MALDI process of insoluble proteins using a combination of a UV nitrogen laser and a tunable mid-infrared (MIR) free electron laser (FEL) was reported. Since the FEL is a very large and expensive equipment, we have developed a tabletop laser source which can generate both UV and tunable MIR lasers. A tunable MIR laser (5.5-10 &mgr;m) was obtained by difference frequency generation (DFG) between a Nd:YAG and a tunable Cr:forsterite lasers using two AgGaS₂ crystals. The MIR laser can generate pulses with an energy of up to 1.4 mJ at a repetition rate of 10 Hz. A UV laser was obtained by third harmonic generation of a Nd:YAG laser splitted from that used for DFG. A time interval between the UV and the MIR laser pulses can be adjusted with a variable optical delay.

We report the design, fabrication, and experimental demonstration of active narrowband multiple wavelength filters in aperiodically poled lithium niobate (APLN) crystals. We obtained the simultaneous transmission of 8 ITU standard wavelengths with transmittance of >90% (~100% in design) and a bandwidth of ~0.45 nm from a 5-cm long APLN Solctype filter. Four peak-narrowed and highly sidelobe-suppressed second-harmonic generation (SHG) signals of four telecom wavelengths from a monolithic LiNbO₃ crystal cascading a 1-cm long APLN wavelength filter and a 1-cm long APLN wavelength converter was also obtained.

Zincblende semiconductors (GaAs, GaP) show great potential for quasi-phase-matched (QPM) THz generation because of their small (20 times less than in lithium niobate) absorption coefficient at terahertz frequencies, small mismatch between the optical group and THz phase velocities, high thermal conductivity, and decent electro-optical coefficient. Terahertz-wave generation was demonstrated recently in QPM GaAs, using optical rectification of femtosecond pulses. Here we report on a new efficient widely tunable (0.5-3.5 THz) source of THz radiation based on quasi-phase-matched GaAs crystal. The source is based on difference frequency generation inside the cavity of a synchronously pumped near-degenerate picosecond OPO and takes advantage of resonantly enhanced both the signal and the idler waves. THz average power as high as 1 mW was achieved in a compact setup.

Non-linear optical wavelength conversion of near-infrared lasers within optical parametric oscillators (OPOs) offers a route to powerful tunable sources in the mid-infrared (mid-IR). Engineered quasi-phasematched (QPM) non-linear optical materials based on gallium arsenide (GaAs) offer an alternative to conventional birefringently phasematched single-crystal materials such as ZnGeP₂, which are currently used in mid-IR OPOs. QPM GaAs crystals have been assembled from commercially available, high-optical quality 100-micron thickness gallium arsenide (GaAs) wafers using a novel glass-bonding (GB) process. This uses thin layers of an infrared transmitting glass (refractive index matched to GaAs) deposited onto each GaAs wafer, which, when heated under pressure, fuse the wafers together to form a monolithic structure. By varying the thickness of the deposited glass layers, the dispersion in the glass can be used to compensate for variations in GaAs wafer thickness and to fine tune the phasematching wavelengths of the QPM crystal. GBGaAs crystals with up to 100 layers have been designed and built for wavelength conversion from 2 &mgr;m into the mid-IR. We report the performance of these crystals used as optical parametric amplifiers (OPAs) in the mid-IR, when pumped by a 2.094 &mgr;m source, and compare these results to measurements for a ZGP OPA. In addition, the dependence of conversion within GBGaAs crystals on the polarisation state of the amplifier seed beam has been investigated along with the temperature dependence of the optimum operating wavelength. Good agreement between experimental results and performance predictions obtained from a numerical model is observed.

Noncollinearly phase-matched optical parametric amplifiers (NOPAs) - pumped with the green light of a frequency doubled Yb-doped fiber-amplifier system ^{1, 2} - permit convenient generation of ultrashort pulses in the visible (VIS) and near infrared (NIR) ³. The broad bandwidth of the parametric gain via the noncollinear pump configuration allows amplification of few-cycle optical pulses when seeded with a spectrally flat, re-compressible signal. The short pulses tunable over a wide region in the visible permit transcend of frontiers in physics and lifescience. For instance, the resulting high temporal resolution is of significance for many spectroscopic techniques. Furthermore, the high magnitudes of the peak-powers of the produced pulses allow research in high-field physics. To understand the demands of noncollinear optical parametric amplification using a fiber pump source, it is important to investigate this configuration in detail ⁴. An analysis provides not only insight into the parametric process but also determines an optimal choice of experimental parameters for the objective. Here, the intention is to design a configuration which yields the shortest possible temporal pulse. As a consequence of this analysis, the experimental setup could be optimized. A number of aspects of optical parametric amplifier performance have been treated analytically and computationally ⁵, but these do not fully cover the situation under consideration here.

We analyze the phase-matching properties of the monoclinic nonlinear crystal BiB₃O₆ (BIBO) for optical parametric amplification of femtosecond pulses when pumped near 800 nm by Ti:sapphire based laser systems. BIBO possesses higher figure of merit than &bgr;-BaB₂O₄ (BBO) and extremely large parametric gain bandwidth for collinear interaction. Experimentally, we compare type-II BIBO and BBO in a double pass optical parametric amplifier (OPA), pumping by amplified 80-fs pulses near 800 nm at a repetition rate of 1 kHz. The conversion efficiency obtained with BIBO is higher and a total energy output (signal + idler) of about 80 &mgr;J is obtained in the plateau region of the tunability curve (1-3 &mgr;m) with an uncoated sample, for a total pump energy of 375 &mgr;J. Shorter pulse durations were obtained with BIBO: e.g. 120 fs (FWHM) near 3 &mgr;m for the idler pulses. Substantial power scaling of such a femtosecond OPA is possible using a large aperture BIBO crystal in the second stage and we demonstrate a total energy output (signal + idler) exceeding 1 mJ, corresponding to an intrinsic conversion efficiency of ≈32% for the second stage, using a specially designed high-power Ti:sapphire pump system operating at 1 kHz. The tunability extends in this case from 1.1 to 2.9 &mgr;m. The high parametric gain and broad amplification bandwidth of type-I BIBO allow the maintenance of the pump pulse duration, leading to pulse lengths less than 140 fs, both for the signal and idler pulses, even at such high output levels.

We report compact sub-mW mid-infrared (IR) laser sources based on difference frequency generation (DFG) in a quasiphase matched (QPM) LiNbO₃ (LN) waveguide directly pumped with two laser diodes (LDs). The mid-IR lasers operate in the cw mode at ambient temperatures, and can be used for the tunable diode laser absorption spectroscopy (TDLAS). To construct the mid-IR laser sources, we employed a fiber-pigtailed wavelength conversion module, which we spliced to a direct-bonded QPM-LN ridge waveguide by using the V-groove connection technique. The modules had high external conversion efficiencies of 10 and 16 %/W for 3.4 and 2.6 &mgr;m, respectively. The signal was obtained from a 1.55-&mgr;m-band distributed feedback (DFB)-LD, and the pump from a single-mode LD stabilized with a fiber-Bragg-grating (FBG). We used 1.064 and 0.976-&mgr;m pump LDs for 3.4 and 2.6-(micron)m generation, respectively. The two LDs and the wavelength converter were assembled with a polarization maintaining fiber, and then packaged in a box. We obtained high outputs of up to 0.20 mW for the 3.4-&mgr;m laser source and 0.33 mW for the 2.6-&mgr;m laser source, and detected CH₄ and H₂O absorption lines with the 3.4 and 2.6-&mgr;m laser light sources, respectively.

A continuous wave singly resonant optical parametric oscillator (CW SRO) has been developed which produces a total of 8.6 Watts of single frequency output at two wavelengths. 5.1 Watts of signal output at 1.65 microns and 3.5 Watts of idler output at 3.0 microns was measured, using a 15 Watt, single frequency fiber laser pump source. Power stability of 3% peak to peak was measured over a period of 24 hours and six hours of operation without longitudinal mode hops was recorded. The beam quality of both outputs was near-diffraction-limit, with an M² parameter < 1.1.We have also observed for the first time, the transition from single frequency to broadband oscillation of a CW SRO at pumping levels greater than three times threshold. At the highest pumping levels, Raman conversion of the signal frequency was observed. Based on these measurements we have been able to define an optimum operating point for CW SROs ensuring maximum conversion efficiency and single frequency oscillation.

We show that it is possible to use of a train of counterpropagating light pulses to enhance the coherent upconversion of intense femtosecond lasers into the extreme ultraviolet (EUV) region of the spectrum. This all optical quasi-phase-matching uses interfering beams to scramble the quantum phase of the generated EUV light, suppressing the contribution of out-of-phase emission. Selective enhancement of up to 600X is observed at photon energies of ~70 eV using argon gas and ~ 150 eV using helium gas.

Narrow-band, multi-cycle terahertz (THz) pulses have been generated in the pre-engineered domain structure of periodically-poled lithium niobate (PPLN) crystals. The mechanism for THz generation is quasi-phase-matching (QPM) optical rectification. Recently, THz generation of high conversion efficiency in a new material, QPM GaAs, were demonstrated using mid-IR femtosecond pulses. GaAs has several advantages for QPM THz wave generation, as compared to PPLN. First, it is highly transparent at THz frequencies (absorption coefficient below 1.5 THz < 1 cm^-1). Second, the mismatch between the optical group velocity and THz phase velocity is much smaller: the corresponding group (ng) and refractive (n) indices are ng=3.431 at 2&mgr;m and n=3.61 at 1 THz. In this work, we report on generation of THz wave packets in three different types of QPM GaAs, combined with their coherent detection using two-color THz time-domain spectroscopy. The QPM GaAs structures are optically-contacted GaAs, diffusion-bonded GaAs, and all-epitaxially-grown orientation patterned GaAs. The QPM optical rectification in GaAs is a nonresonant mechanism, as opposed to widely used photoconductive antenna technique in GaAs, where THz radiation is produced via ultrafast charge transport caused by photoexcitation with femtosecond laser pulses of the near-IR range. In order to avoid linear and two-photon absorption in GaAs, we use 2&mgr;m femtosecond pulses to generate THz pulses. We measure the THz waveforms via electro-optic sampling in ZnTe using 0.8&mgr;m probe pulses. The corresponding power spectra are also measured by a THz Michelson interferometer. Frequency tunability in the range 0.8-3 THz is achieved with several structure periods.

We report on an optical parametric amplification system which is pumped and seeded by fiber generated laser radiation. Due to its low broadening threshold, high spatial beam quality and high stability, the fiber based broad bandwidth signal generation is a promising alternative to white light generation in bulky glass or sapphire plates. We demonstrate a novel and successful signal engineering implemented in a setup for parametric amplification and subsequent recompression of resonant linear waves resulting from soliton fission in a highly nonlinear photonic crystal fiber. The applied pump source is a high repetition rate ytterbium-doped fiber chirped pulse amplification system. The presented approach results in the generation of ~50 fs pulses at MHz repetition rate. The potential of generating even shorter pulse duration and higher pulse energies will be discussed.

We demonstrate a novel terahertz (THz) pulse shaping technique, which guarantees ultimate flexibility for arbitrary THz pulse generation. The THz pulse shaper consists of a fanned-out periodically-poled lithium niobate (FO-PPLN) crystal-the domain width of the FO-PPLN crystal varies continuously across the lateral direction-, a spatial mask, and a spherical mirror. Optical pulses are line-focused on the FO-PPLN crystal to generate spatially separated multi-frequency components of THz pulses. The spatial mask is placed in front of the FO-PPLN crystal in order to manipulate the spatial pattern of the incident optical beam, thus to control the amplitudes of the spatially dispersed THz frequency components. Spectral resolution of this method is determined by FO-PPLN bandwidth and mask resolution: estimated practical resolution is ≈0.01 THz for 1 THz bandwidth. After the spherical mirror assembles the various frequencies into a single collimated beam, a shaped THz pulse can be obtained, with the pulse shape determined by the Fourier transform of the pattern transferred by the mask. As a proof-of-principle experiment, we measured THz waveforms using metal masks. The experiment was performed using 800-nm, 100-fs pulses from a 1-kHz Ti:sapphire regenerative amplifier. We used a 5-mm long FO-PPLN sample (width = 10 mm, height = 0.5 mm) continuously tunable from 0.6 to 1.5 THz. We tested the metal masks of three different spatial patterns: low-pass filter, high-pass filter, and double slit. The experimental results show that the THz waveforms are determined by the spatial patterns of the masks.

Optical fiber parametric amplification is combined with Raman amplification to demonstrate the possibility of extending the flat gain bandwidth of Raman fiber amplifiers. Counter propagating pumps separated by over 145 nm are used to pump a section of highly nonlinear fiber. Parametric gain enables an increase in the gain bandwidth by extending the gain region to the long wavelength side of the Raman gain. Gains of nearly 20 dB have been achieved with this configuration. To achieve gain flatness of 5-6 dB, lower peak gains of between 8 and 14 dB are observed where the variations of the gain and gain flatness are controlled by adjusting the two pump powers. Optimal pump powers are determined that result in good performance amplification by characterizing the receiver power penalty of bit error rate measurements. Negligible power penalty is observed in the region of strong Raman gain whereas nearly a 3 dB power penalty is observed in the region of strong parametric gain. An experimental technique is proposed that helps in the understanding of the coupling of the parametric and Raman processes.

We present a numerical model of a multi-crystal approach that increases the quantum efficiency of a parametric amplifier. Here is a two-crystal approach where the second stage crystal uses the signal energy from the first stage to amplify the desired idler wavelength. The numerical model allows for arbitrary input beam profiles and it can accommodate multiple crystals and optical elements. In this study a pair of PPLN crystals was modeled leading to more than double the idler output energy. The maximum M² value for the output idler beam calculated was 5.2.

Orion is a new laser facility under construction at AWE for studying high energy density physics whose design has been underwritten by modelling various aspects of the beamlines. For the long pulse beams this has included the frequency conversion process from the first to the third harmonic. The need to take account of the effect of the phase modulation applied for Smoothing (of the output focal spot) by Spectral Dispersion (SSD) has led to the development of a four-dimensional (x,y,z,t) frequency conversion code. The code uses a split-step approach, considering diffraction, walk-off, coupled waves, wavefront error, angular dispersion, self-phase modulation, and group velocity dispersion. The code's performance is demonstrated using an idealised input beam and the Orion frequency conversion crystal design. Without the presence of phase modulation, the code reports a third harmonic conversion efficiency of 79.2%. With phase modulation, a conversion efficiency of between 70.3% and 71.6% is reported, depending on the directions of applied angular dispersion. The smoothing of the focal spot as a function of time using a kinoform phase plate is also demonstrated based on the 2D-SSD system to be used on Orion. The contrast ratio of the focal spot is shown to reduce by a factor of 5 within the first 0.2 ns, and to reach 7% by the end of the 1.25 ns time window.

We present a novel numerical model that allows determining the Stokes and anti-Stokes emission characteristics of a continuous-wave silicon-based Raman laser. This so-called iterative resonator model evaluates for every half roundtrip time the longitudinal distribution of the intra-cavity pump, Stokes and anti-Stokes fields propagating in forward and backward directions, while taking into account the two-photon absorption losses and free carrier absorption losses occurring in the silicon laser medium. Furthermore, we demonstrate that our model exhibits important advantages in comparison with the power distribution model used for silicon-based Raman lasers. Finally, we present the first numerical simulation results for a silicon-based Raman laser emitting both Stokes and anti-Stokes photons.

A novel third-order optical parametric oscillator (OPO) based on four-wave mixing process in bulk TiO₂ crystal is theoretically characterized. The OPO is assumed to be synchronously pumped by pulses of either 100 fs duration at 800 nm or 100 ps at 1.06 &mgr;m. For the former case, its signal is tunable from 0.45 to 0.8 &mgr;m by changing the crystal orientation; for the latter case, the OPO is tunable from approximately 0.6 to 1.06 &mgr;m. The threshold conditions are also calculated considering the effect of group velocity mismatch (GVM) between the pump pulse and the signal (or idler) pulse. The threshold is dependent on signal wavelength since GVM increases as signal wavelength decreases. Using a 2 mm-length crystal and assuming optimum focusing, the threshold for the singly resonant condition is 710 mW at 700 nm for the former case and 93.6 W for all the signal wavelengths for the latter case. The threshold condition is also calculated assuming different pumping pulse widths. The result shows the ideal pulse width is around 2 ps, for which the threshold power is 1.42 W for all the signal wavelengths.

Frequency modulation (FM) techniques are well known methods for improving signal-to-noise ratios in laser spectroscopy. Such techniques have proven particularly effective with diode lasers due to the ease with which they can be frequency modulated via their injection current. Although singly-resonant optical parametric oscillators (OPOs) are flexible, powerful and widely-tunable sources for mid-infrared laser spectroscopy, the utilization of FM techniques with OPOs suffers from the inconvenience of requiring an external mid-IR modulator. As a consequence, FM techniques have not been implemented with such devices. In this paper we describe the implementation of wavelength-modulation spectroscopy (WMS) and frequency-modulation spectroscopy (FMS) using a singly-resonant OPO pumped by a fiber-amplified diode laser. The OPO was capable of producing output powers of up to 1W in the 3.15-3.8 &mgr;m range with continuous tuning over >100GHz on millisecond timescales. Frequency modulation, via injection current, of the diode laser transferred directly to the OPO's idler output, allowing mid-IR FM to be achieved without external modulation devices. WMS and FMS spectra of methane were then recorded, clearly demonstrating that this approach provides a means of implementing these important techniques with powerful, widely tunable, mid-IR sources while retaining the simple, flexible modulation properties of diode lasers.

Fabrication of quasi-phase-matching (QPM) gratings suitable for cascading of two second-order parametric nonlinear processes in a single lithium niobate crystal is being undertaken using a new technique - electric field poling assisted by laser micro-machined topographical electrodes. To date, single period poled gratings with 45.75, and 45.8 &mgr;m periods have been fabricated in order to demonstrate second harmonic generation of 1064nm laser light with 1^st order type-I and 7^th order type-0 QPM simultaneously. The two frequency doubling processes share a common Z polarized second-harmonic wave which allows exchange of energy between the two orthogonally polarized fundamental waves and several second order cascading interactions can be realized. The use of the higher QPM orders (3rd, 5th or 7th) for the type-0 second harmonic generation process leads to comparable efficiencies of the two processes, as the respective nonlinear coefficients are d_zzz ~27 pm/V and d_yyz ~ 4.7 pm/V in lithium niobate crystals. Possible applications include; polarization switching, parametric amplification and polarization mode dispersion monitoring, and polarization insensitive second harmonic generation.

In the past two decades mid-IR nonlinear optical crystals have grown from scientific curiosities to practical robust materials generating efficient, multi-watt output in the 3-12&mgr;m spectral range. Nonetheless, improved NLO crystals are critical for further advancing mid-IR laser development. In particular, mid-IR materials are needed which: 1) efficiently convert cw pump sources; 2) can be pumped with 1-micron (Nd and Yb) lasers; and 3) offer improved performance in the 8-12 micron range and beyond. For such applications a high nonlinear coefficient is desirable, but this is less important than more practical properties such as low absorption loss, high laser damage threshold, low thermal lensing, and non-critical phase matching (NCPM). To meet these demands, the search for improved mid-infrared NLO crystals is proceeding on three fronts. First, work continues to reduce losses in the best existing materials such as ZnGeP₂, AgGaSe₂, and CdGeAs₂. Secondly, new compounds such as AgGaGeS₂ and AgGaGe₅Se₁₂ are being evaluated. Thirdly, and most promising, is the work on all-epitaxial processing of orientation-patterned gallium arsenide (OPGaAs) and other binary quasi-phase-matched semiconductors such as ZnSe, GaP, and GaN. This review paper will discuss recent advances on all of these fronts.

Results of our SRS investigations of the organic crystals &agr;-Ca(HCOO)₂ (alpha calcium formate), LiNH₂C₆H₄SO₃ • H₂O (lithium sulfanilate monohydrate) and N(CH₂CH₂NH₃)₃Br₃ (tren trihydrobromide) are presented. Currently a promising development in solid-state laser physics is the use of highly transparent ceramics. We have demonstrated efficient SRS in three ceramics based on cubic rare earth sesquioxides RE₂O₃ (RE = Sc, Y and Lu) with Raman shifts in the range of 378 cm^-1 to 419 cm^-1. Cascading &khgr;⁽³⁾ → &khgr;⁽²⁾ → &khgr;⁽³⁾ lasing effects, self-SHG, self-SFM and cascading Stokes and anti-Stokes generation between phonons of different energies has been observed in Li₂SO₄ • H₂O (lithium sulphate monohydrate), CsLiMoO₄ (caesium lithium molybdate) and CsLiMoO₄ • 1/3H₂O.

We present the first modeling results for the Stokes and anti-Stokes output of a mid-infrared continuous-wave silicon-based Raman laser. These emission characteristics are generated by the use of an iterative resonator model, the loss terms of which we adapted for the case of silicon-based Raman lasers operating in the mid-infrared spectral domain. These loss terms contain besides linear losses also the three-photon absorption losses that occur in this type of lasers. We discuss the behavior of this three-photon absorption mechanism and its influence on both the Stokes and anti-Stokes output. Finally, we compare these emission characteristics with the corresponding simulation results for a near-infrared silicon-based Raman laser in which linear losses, two-photon absorption losses and free carrier absorption losses occur.

Integral expressions for the pump and generated fields are presented here for the case of second harmonic generation of a focused Gaussian pump beam incident on a nonlinear crystal . The birefringent walk-off of the generated beam and the effect of pump depletion are included in the theory.

The field of Nonlinear Optics has provided many techniques to characterize photonic materials. The Z-scan method is a well estabileshed technique that exploits front wave distortions of the light beam to determine the nonlinear properties of optical materials. Several variations of the methods have been developed, as the eclipse Z-scan that can provide up to two orders of magnitude higher sensitivity than the original Z-scan set-up. We report a new variation of the Z-scan method to characterize the third-order optical nonlinearity of photonic materials. By exploiting the combination of the eclipse Z-scan with thermal nonlinearity management, we demonstrate an improvement in sensitivity and flexibility of the method to simultaneously characterize the thermal and nonthermal nonlinearity of optical materials. The method is demonstrated by measuring the nonlinear refractive index in CS₂, SiO₂ and H₂O as standard materials, and also of a biomaterial, the amino acid Tryptophan in water solution, using the same experimental set up based on a femtosecond Ti-saphire laser operating at 76MHz repetition rate.

In the present paper, using the hydrodynamic model of semiconductor plasmas and following the coupled mode approach an analytical investigation of the stimulated Raman (SRS) and Brillouin (SBS) scatterings of the Stokes mode is undertaken in magnetoactive doped III-V semiconductors. These phenomena have been studied considering that the second-order forces responsible for them are different, viz., the finite differential polarizability gives rise to SRS, while the material properties like piezoelectricity and electrostrictive strain produces SBS in the medium. Gain coefficients, threshold pump intensities, and optimum pulse durations for the onset of SRS and SBS are estimated. The qualitative behavior of transient gain coefficients is found to be in agreement with the experimental and other theoretical observations. The proper selection of doping concentration and an externally applied magnetic field substantially enhances the gain coefficients of SBS and SRS processes. The ratio between the two gain constants indicates that for the same pump field SBS exhibits higher gain than SRS by two orders of magnitudes. The analysis explains satisfactorily the competition between stimulated Raman and Brillouin processes in the short- and long-pulse duration regimes. Numerical estimates have been made for n-type doped InSb crystal at 77K duly irradiated by 10.6&mgr;m CO₂ laser.

Widely tunable parametric oscillation has been obtained in the temperature-tuned, z - cut, 90^o phase-matched B_iB₃O₆ pumped by a Nd:YAG laser. Tuning range was 1.625~ 3.083&mgr;m at the crystal temperature of 20^o~190^o C. These data were used to reconstruct the high-accuracy Sellmeier and thermo-optic dispersion formulas in the 0.474~3.083&mgr;m range that give an excellent reproduction of the phase-matching conditions thus far reported in the literature.

We have demonstrated the 90° phase-matched type-I difference-frequency generation (DFG) in AgGa_1-xIn_xS₂ with x = 0.14 by mixing the dual-wavelength pulses emitted from an electronically tuned Ti:sapphire laser. Infrared radiation continuously tunable over the range of 4.8-6.98&mgr;m was generated by independently varying the two wavelengths in the spectral range of 705-932nm. In addition, 4.04&mgr;m radiation was generated by mixing a Nd:YAG laser with the Ti:Sapphire laser in the same crystal. Sellmeier equations that reproduce well the experimentally obtained data for these processes are presented.

This paper reports the experimental results on the phase-matching properties of AgGaGeS₄ for second-harmonic generation (SHG) at 0.8 &mgr;m that was achieved by using the KTP optical parametric oscillator and difference-frequency generation (DFG) at 2 and 5-12 &mgr;m that were achieved by using the dual-wavelength emitting Ti:Sapphire laser and the Nd:YAG laser. Two AgGaGeS₄ samples showed locally different phase-matching conditions which were probably caused by the various crystal compositions. The new Sellmeier equations were constructed using the literature value of the refractive indices and compared with the experimental data. A satisfactory agreement between the model calculation and the experiments is obtained.

An intra-extra (hybrid) cavity Optical Parametric Oscillator (OPO) using monolithic KTP crystal has been built for converting 1064nm Nd:YAG laser radiation into 1572nm eye safe wavelength with high total conversion efficiency. Here a monolithic X-cut KTP crystal, having HR coating for 1064nm on the output face, was used external to the Nd:YAG laser. The Nd:YAG laser is Q-switched by a rotating prism. Because of the prism in rotation, it comes in alignment with the PR (partial reflective) mirror of Nd:YAG laser and with the output face of the KTP crystal. This situation gives rise to the intra-extra cavity OPO. In this configuration OPO gives sufficient eye safe output even when Nd:YAG is operated below its lasing threshold. Also the power of the OPO eye safe output is reasonably insensitive to the alignment variations.

We investigated spectral broadening in a standard fiber using a nanosecond directly modulated DFB laser (&lgr;=1549 nm), amplified by a two stage Erbium-doped fiber amplifier. The amplifier provided amplification of 2-mW peak power input pulses to 100-W peak power output pulses. In other hand, the directly modulation of DFB lasers caused transient oscillations at the beginning of pulses. In our case pulses consisted of a 2-ns transient part followed by a steady-state plateau. We used a monochromator to measure the spectrum at the fiber output. A fast photodetector was placed at the monochromator output and pulse shapes were measured for different wavelengths. This technique allowed the separate measurement of different parts in output pulses spectrum. We used the SMF-28 fiber with the standard dispersion of 20 ps/nm-km for our wavelength. We made measurements of the output spectra for three fiber lengths: 0.6-km, 4.46-km and 9.15-km; finding that the initial transient part of a pulse shows supercontinuum generation whereas the plateau results in conventional Raman amplification of this supercontinuum.

In the present work, demonstrated for the first time is automatic quasi-smooth scanning of an resonant doubler cavity synchronously with the frequency of a CW auto-scanned Ti:Sapphire laser within a 1-THz frequency range (2 THz for second harmonic), which is limited only by the spectral acceptance bandwidth of non-linear crystal. Significant (more than by an order of magnitude) widening of the synchronous scanning range was achieved owing to the suggested method of automatic re-locking of the external cavity. The number of automatic cycles when the input frequency is relocked to different transmission peaks of the doubler cavity can be arbitrarily large, and the domain of automatic quasi-smooth frequency scanning that is composed of multiple smooth scanning ranges (~ few GHz wide). The doubler was tested with bow-tie-shaped ring cavity configuration and LBO/BIBO crystals. Doubling efficiency was in the range of 25-42% at input power of 0.7-2.1 W.

We generate mid-infrared pulsed light tunable between 5.6 &mgr;m and 6.6 &mgr;m using an optical parametric oscillator (OPO) directly pumped by a Cr,Tm,Ho:YAG, Q-switched laser operating at 2.1 &mgr;m. The Holmium laser uses a RTP Q-switch to produce pulses shorter than 100 ns and energies of up to 42 mJ in a single spatial transverse mode at a repetition rate of 5 Hz. To our knowledge this is the first report on a lamp pumped Cr,Tm,Ho:YAG laser using a RTP crystal as an electro-optical Q-switch. The OPO is based on a ZnGeP₂ (ZGP) crystal cut for type I phase matching. The singly resonant OPO (SRO) uses a linear cavity consisting of two plane mirrors to minimize the required pump flux to reach threshold. The SRO has a threshold of 2.4 mJ, a maximum idler pulse energy of 3.1 mJ, and is tunable from 5.6 to 6.6 &mgr;m. Operation in this wavelength range, combined with wide tuning and a high pulse energy makes this SRO particularly suitable for tests in the field medical application, e.g., for cutting of soft tissue during surgery or corneal corrections.

Some physical aspects of realizing one-, two-, and three-phonon scattering of light in the Bragg regime under specially chosen conditions in optically anisotropic tellurium dioxide crystal are considered. The exact and closed analytical models for describing these regimes using diagram technique of describing the orders of scattering are exploited. The performed analysis is devoted first of all to the efficiency of light scattering in these regimes and is illustrated by numerical estimations. Then, reasonable attention is paid to the effect of acoustic anisotropy in TeO₂ -single crystals.

Optical parametric generator (OPG) is a very attractive optical down-conversion configuration since it is a single pass process and no cavity mirror's alignment is required. Thus the system configuration is much more simple and robust. Traditionally, OPG processes were demonstrated using a pump source with a pulse length of the order of picoseconds or less. This is because GW/cm² order of magnitude pump irradiance was required to excite an OPG process, and such irradiance in nanosecond long pulses commonly damages the non-linear crystal. The introduction of periodically poled crystals with high non-linear coefficients has significantly lowered the threshold for parametric processes. This progress in non-linear crystals enables exciting OPG processes at less than 100MW/cm² irradiance, using nanoseconds long pulses from Q-switched lasers. We present an OPG with a threshold of less than 10 MW/cm² using an 80 mm long Periodically Poled Lithium Niobate (PPLN) non-linear crystal. High signal conversion efficiency and high power were obtained at 25 nanosecond pulse length, 10 kHz repetition rate pumping without damaging the crystal. Theoretical approaches for explaining this OPG regime are discussed.

Mechanisms of nonlinear optical limiting by fullerenes and fullerene-like nanostructures in solutions, suspensions theoretically and experimentally investigated in wide spectral range 0.3-1.1 &mgr;m. An essential contribution of photoinduced scattering to nonlinear optical limiting was demonstrated in fullerene solutions and in suspensions of fullerene-like nanostructures. It is shown than suspensions based on fullerene-like nanostructures are the most perspective for devices design with nonlinear optical protection from laser radiation (speed less than 1 ns, dynamic range 10³-10⁴, limiting threshold 5x10^-6 J/cm², spectral range 0.3-1.1 &mgr;m, color-comfortable vision through it, i.e. the absence of limiter color.) Devices with nonlinear optical limiters are demonstrated. The computer simulation of femtosecond range optical switchers, based on fullerene containing media was performed. Fabri-Perot interferometers, containing film of fullerene film, produced by vacuum deposition and film of fullerene-polymer solid solution were investigated. Fullerene polarization nonlinearity leads to light-induced refractive index change. The probability of interferometer reflection and transmission control by low intensity signal is demonstrated.