A review of measurement techniques and nonlinear coefficient values are presented. Coefficients of a few materials are evolving as standards by consensus based on independent measurements. Improved instrumentation, extension of measurement techniques, and more detailed analysis are improving accuracy in recent measurements. Confusion still remains for values of some materials, and specification of the reporting frame for the tensor values remains an issue.

Zinc germanium diphosphide (ZnGeP₂) is a nonlinear optical material useful for frequency conversion applications in the midinfrared. A broad absorption band peaking near 1.2 microns and extending past 2 microns is often observed. To identify the defects responsible for these absorption losses, we have performed an optical absorption investigation from 10 to 296 K on bulk crystals of ZnGeP₂ grown by the horizontal gradient-freeze method. Three broad absorption bands in the spectral range from 1 to 4 microns are observed that are due to native defects. Comparison of photoinduced changes in absorption with photoinduced changes in EPR spectra allowed specific defects to be associated with each of the three absorption bands. A band peaking near 1.2 microns and another band peaking near 2.2 microns involve transitions associated with singly ionized zinc vacancies. A third absorption band, peaking near 2.3 microns and extending from 1.5 microns to beyond 4 microns, involves neutral phosphorus vacancies. Absorption bands due to anion-site donor impurities Se and S have also been studied.

CdGeAs₂ is an important nonlinear optical infrared material. Room-temperature absorption and temperature-dependent photoluminescence (PL) of as-grown p-type bulk crystals and crystals doped with indium and tellurium have been measured. The intensity of an intervalence band absorption near 5.5 microns (0.225 eV) is correlated with the intensity of a PL band near 0.55 eV. Both of these optical features indicate the presence of a native shallow acceptor level at 120 meV above the top valence band. The 0.55-eV PL band is donor-acceptor-pair recombination between shallow donors and the shallow acceptor level. A second PL band peaking near 0.35 eV is donor-acceptor-pair recombination between shallow donors and a deeper acceptor at 300 meV above the top valence band. Doping with indium and tellurium produces n-type material. The intervalence band absorption at 5.5 microns is completely eliminated in the n-type samples. Indium donors are incorporated on the Cd site and Te donors are incorporated on the As site.

The periodic poling of stoichiometric lithium tantalate, a nonlinear optical material with great promise for the frequency conversion of high-average-power solid state lasers, has been investigated. Two problems with commercially available stoichiometric lithium tantalate substrates have been identified: non-reproducibility of the coercive field from one wafer to the next, and susceptibility to the formation of micro-domain defects. Strategies for dealing with these problems have been developed. Wafer-scale poling has been carried out to produce quasi-phasematching gratings with periods as short as 7.3 microns on half-millimeter thick substrates and 25.4 microns on millimeter-thick substrates. The phase-matching properties of periodically poled stoichiometric lithium tantalate have been measured using nonlinear optical frequency conversion. For processes which generate visible radiation, good agreement with predictions based on the published Sellmeier equation for stoichiometric lithium tantalite has been obtained.

In the last one and a half decade crystals of barium metaborate (β-BaB₂O₄ or BBO) have been widely applied in non-linear optics and electro-optics. The growth of BBO is a technologically sophisticated procedure enabling the production of big high-quality single crystals. The best results have been obtained by growing BBO with top-seeded solution growth (TSSG) method 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 weakening convective flows and 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. Such the nonconventional approach has allowed to carry out the contact free structurization and intensification of convective flows in the melt-solution body and by that to reach more complete crystallization of a material increasing the yield before effect of constitutional supercooling. In that way we grow BBO crystals, from which it is possible to make non-linear optical elements of 15x15x15 mm³ sizes and electro-optical elements for Pockels cell with 6x6x22 mm³ sizes along an optical axis.

KDP and DKDP are unique materials for frequency conversion in large-aperture laser systems. Under high power irradiation, a threshold exists above which multiple damage sites are formed in the bulk of crystal plates thus obstructing beam propagation and creating undesirable beam modulations. Damage testing has focused on measuring the irradiation threshold fluences that lead to irreversible material modifications. However, small amounts of damage in optical components have been determined not to hinder system performance in large-aperture laser systems. In this work, we present a new approach to evaluating damage performance that provides statistics on damage pinpoint density, size and morphology as a function of fluence, wavelength and pulse duration and relates that to the resulting beam obscuration. We measure the size of damage sites for different wavelengths, pulse-lengths, and fluences. Different pulse-lengths are approximated by using multiple pulses appropriately delayed with respect to each other. We find that in KDP/DKDP crystals, the size of damage sites strongly depend on the pulse-length, with longer pulses creating larger damage sites. Also examined are ways of laser-annealing to increase the damage resistance.

We have demonstrated operation of an optical parametric oscillator (OPO) pumped by a coiled multi-mode fiber amplifier. Coiling of multi-mode fiber amplifiers is a simple technique that allows the output from diode-pumped fibers to be substantially increased relative to that from a standard single-mode fiber, while maintaining the diffraction-limited beam quality. Pulse energies from such fiber amplifiers are high enough to drive nonlinear optical processes. Here we report efficient frequency down-shifting of such a device using an OPO. A diode-pumped Yb-doped fiber was used to amplify 1 microjoule, 20 nanosecond pulses from a 1.064μm Nd:YVO₄ laser to a level of up to 107 microjoules in a single transverse mode, polarized beam. The 6m-length fiber had a 200 micron diameter cladding and a 25 micron core. An unpolarized output of 5.6 Watts was measured for 13 Watts of 976nm diode pump input. Oscillation of a periodically-poled lithium niobate (PPLN) OPO was observed with an oscillation threshold pump pulse energy of 31 microjoules. Up to 0.63 Watts of 1.5μm OPO signal output was measured with 2.6 Watts of incident pump, at a repetition rate of 24kHz. Tuning of the OPO signal wavelength was performed between 1.5 and 1.6μm.

We present recent experimental and simulation results for broad-band, off-axis infrared light generation by a parametric down-conversion process. We use a periodically poled lithium niobate in the experiments. Our simulations explore the competition between on-axis and off-axis signal generation. We explore the contrast between a narrow pump and a broad pump on the emission spectrum.

We’ve demonstrated a nanosecond KTA OPO utilizing a high Fresnel-number quasi-monolithic image-rotating nonplanar-ring optical cavity to efficiently generate 1550 nm light with beam quality M²~4. The OPO was pumped at 1064 nm and injection-seeded at 1550 nm and was tested using either one or two 10×10×17 mm³ KTA crystals. Total measured conversion efficiencies were as high as 45% and 55% respectively, with corresponding 1550 nm energies of approximately 135 mJ and 170 mJ. While energy and efficiency were high, agreement with numerical models that included walkoff, diffraction, and geometry of the nonplanar-ring, was poor near the oscillation threshold. Single-crystal oscillation revealed different thresholds for each KTA crystal. When tested by observing unphasematched 2ω generation, each crystal appears to contain a single ferroelectric domain, suggesting that refractive index inhomogeneity, or some other type of defect, prevents perfect phasematching.

Recently there has been interest in producing "cubic-like" effects, such as self-focusing, in materials engineered to have a rapidly oscillating quadratic nonlinearity. If the nonlinearity oscillates on a fast enough scale, the governing quadratic equations can be effectively averaged to give cubic equations. We propose a multiple scales approach in which diffraction is neglected at leading order. In doing so, we obtain exact solutions to the leading order. In doing so, we obtain exact solutions to the leading order system and solvability conditions on the slow evolution and transverse spatial dependence which, ensure that the higher order corrections are periodic. Using a variational approach, dynamics and stability of the solutions to the slow evelope equations are described.

We consider the mean field model of the optical parametric oscillator (OPO) when the second harmonic of the OPO is driven externally by a spatially periodic pump field. Exact solutions for the first and second harmonics can be derived using Jacobi elliptic functions. These solutions can describe behavior that is both sinusoidally varying as well as front and pulse-like in the transverse direction. Numerical simulations show that for a wide range of parameter space these solutions are stabilized transverse field structures. Bifurcations can also occur which result in new nontrivial, but periodic, spatial structures.

The third harmonic frequency conversion efficiency curves of Gaussian beams similar to Flattened Gaussian beams(FGB’s) having increasing integer N were obtained. The efficiency curves versus the crystal lengths, the pumping wave polarization ratio, the order of the FGB’s and the pump power intensity have been calculated by computer simulation. The conversion efficiency of third harmonic generation of the Flattened Gaussian and Gaussian beams were obtained in detail numerical stimulation for CsLiB6O10. The conversion efficiencies of 96% of the flattened Gaussian are larger than that of Gaussian efficiencies of 88% in type-II (1) phase matching.

The advent of novel quasi-phase matched materials based on patterned growth gallium arsenide offer the possibility of broadly tunable IR sources covering the long- (5-12μm) and mid-wave (3-5μm) infrared spectral regions. From the standpoint of chemical sensing, the long-wave infrared region between 8-12μm is attractive since it is an atmospheric window, many functional groups absorb in this region and absorptions tend to be strong compared to the mid-IR. We are employing orientation patterned GaAs as part of cw difference frequency spectrometer. In this system, light from two, tunable external cavity diode lasers covering the 1.3μm and 1.5μm telecom bands was amplified then mixed in an orientation- patterned GaAs crystal, producing radiation in the 7-9μm region. The system serves as a source for a cw cavity ring-down spectrometer for ultra-trace gas detection applications. The combined tunability of the source, coupled with the sensitivity of cavity ringdown spectroscopy will allow both detection and identification of a wide range of species with unprecedented performance.

An all-solid-state infrared trace gas sensor is presented combining a continuous-wave optical parametric oscillator (OPO) with Cavity Leak-Out spectroscopy (CALOS), a cw version of Cavity Ring Down spectroscopy. The PPLN based pump resonant, singly resonant OPO is pumped at 1064 nm (2 W). Dual cavity design allows to select any desired wavelength within the emission range of the OPO (3.1 - 3.8 μm) and to use different tuning schemes in order to scan absorption features. To detect the CALOS signals the OPO frequency is scanned over the cavity resonance at kHz rates. The high power of the OPO (up to 100 mW at each end of the cavity) allows a strong excitation of the TEM00 mode of the cavity, yielding large detector signals. A noise-equivalent absorption coefficient of 1.6*10^-10cm^-1/√Hz is reached for integration times up to 180 sec. This corresponds to a detection limit for ethane at sub-ppt level. Measurements at reduced pressure (100 mbar) combined with a scanning of the OPO over cm^-1 wide regions allows a multi-gas analysis of ambient air and human breath samples without a cooling-trap.

A novel chaotic lidar (CLIDAR) system utilizing optical chaos has been investigated and demonstrated. Compared with conventional pseudo-random code-modulated continuous-wave lidars, CLIDAR has the advantages of very high range resolution and unambiguous correlation profile benefiting from the very broad bandwidth of the chaotic waveform used. In this paper, a CLIDAR system using an optically injected semiconductor laser as the light source is studied both numerically and experimentally. The power spectra, phase portraits, time series, and correlations of the chaotic states obtained at different operating conditions are compared. Chaotic states with flat and smooth spectra are shown to have better performances. The correlation dimension and the largest positive Lyapunov exponent for each chaotic state are computed as well, where the relation between the complexity of chaotic states and peak sidelobe level is discussed. To show the feasibility of CLIDAR, proof-of-concept experiments, including range finding, two-dimensional imaging, and multiple-target detection, are demonstrated. A range resolution of 2 cm, which it is currently limited by the detection bandwidth of the real-time oscilloscope used, is achieved.

In this paper, we propose and demonstrate the application of concepts from digital filter design to optimize artificial optical resonant structures to produce a nearly ideal nonlinear phase shift response. Multi-stage autoregressive moving average (ARMA) optical filters (ring resonator based Mach-Zehnder interferometer lattices) are designed and studied. The filter group delay is used as an alternate measure instead of finesse or quality factor to study the nonlinear sensitivity for multiple resonances. The nonlinearity of a 4-stage ARMA filter is 17 times higher than that of the intrinsic material. We demonstrate that the nonlinear sensitivity can be increased within the same bandwidth by allocating more in-band phase or using higher-order filter structures and that the nonlinear enhancement improves with increasing group delay. We also investigate some possible ways to pre-compensate the nonlinear response to reduce the occurrence of optical bistabilities. The impact of optical loss, including linear absorption and two-photon absorption, and fabrication tolerance are discussed in post-analysis.

We describe the detection of trace amount of ozone in a gas mixture at atmospheric pressure using excitation by the fourth harmonic of a Nd:YAG laser at 266 nm and measurement by photoacoustic detection. We show that a sensitivity of 10 ppbV can be achieved.

Backscattered 2 ω and 3 ω/2 harmonics were investigated during the interaction of femtosecond radiation ( λ=795 nm, t=150 fs, 10-Hz pulse repetition rate) with various targets. The harmonics were generated inside the drilled hole without changing the position of target from shot to shot. No 3 ω/2 harmonic was generated in the case of single shots irradiated the fresh surface of the target. Various characteristics of harmonic radiation were analyzed and their dependences on pump radiation parameters were discussed.

We report a very efficient nonlinear optical conversion in thin films of wide band-gap materials. Very high conversion efficiency to the third harmonic radiation is achieved for an unamplified femtosecond Cr⁴⁺:forsterite laser in a sub-micron-thick film of a nanocrystalline ZnO pulsed-laser deposited on a fused silica substrate. Both the nonlinear optical coefficient and the coherence length are measured for film composed of 10-nm nanoclusters.

In this paper, we introduce a new dispersion management method of realizing exponentially decreasing dispersion fiber by using only two kinds of segments of fibers with different dispersions connected together. Exponentially decreasing dispersion fiber is used to obtain the optimum soliton transmission situation. Some simulation results show that this method has more advantages than conventional soliton system, and can significantly improve the system performance.

The rapid flow of vibrational energy within a molecule is central for the control and as well for the theory of unimolecular reactions. It defines the lifetime of vibrationally excited states and thus the time during which a specific vibrational excitation can control the outcome of chemical reactions. Times for intramolecular vibrational energy redistribution (IVR) can be deduced either indirectly from time-independent high resolution infrared(IR) spectra or measured directly in kinetic pump-probe experiments. We have applied delayed ultraviolet(UV) absorption spectroscopy with a time resolution of 150 fs to measure intramolecular vibrational energy redistribution after near-IR excitation of the CH-stretching vibration around 5900 cm-1 in CF3CHFI, CH3I, C2H5I, and C7H8. Intramolecular relaxation times T(IVR) between 3 and 7 ps have been found in the gas phase. For CH3I an additional short time of 250 fs has been measured. In the liquid phase IVR is followed by a fast collisional energy transfer of the excitation energy to the solvent molecules. Assuming a two step kinetic mechanism intermolecular relaxation times T(transfer) between 10 and 30 ps have been determined.

Numerical model describing transient stimulated Raman scattering and taking into account diffraction was developed and Stokes wave evolution in compressed hydrogen was simulated to study space-time dynamics of amplitude-phase SRS characteristics. Space-time intensity and phase dependencies as well as spectrum and spatial coherence function of pump and Stokes waves were obtained. Considerable difference in mentioned characteristics was found out for transient and quasi-stationary stimulated Raman scattering modes. More complicated space-time dependencies are typical for transient mode in comparison with quasi-stationary mode. However, under quasi-stationary conditions Stokes wave phase varies in wider limits, which results in spatial coherency lowering. Module of spatial coherency function value lowers to threshold and then becomes stable as conversion coefficient increases. Presence of Stokes beam focusing is shown at stimulated Raman scattering, which can be explained by competition of strong Raman amplification and diffraction. Results of simulations are in good agreement with experimental data.

For ns 355nm pumped simple type II BBO OPOs, two problems still remain even after rotated cavity design 1,2. The first problem is that the efficiency is still low. The other problem is the requirement of adjusting the waveplate inserted in the rotated cavity during the wide tuning range. Here, we propose and demonstrate a simple prism rotated cavity1, which uses both a type I and a type II BBO crystals pumped at 355nm.