This paper describes the development of synchronously pumped tandem OPO/OPO (optical parametric oscillator) and OPO/DFM (difference frequency mixing) devices based on a single PPLN crystal. Tandem intra-cavity devices are of interest for efficient conversion from the near-infrared (1.064 μm) to the mid-infrared because back-conversion is reduced and the near-infrared signal beam is also converted to the mid-infrared. The single crystal OPO/DFM device is phase matched by temperature tuning and 4.3 W (3 W at 3.9 μm 1.3 W at 2.35 μm) has been generated in the mid-infrared with a pump power of 25 W at 1.064 μm. The OPO/OPO produced an output power of 850 mW at 3.9 μm and 50 mW at 4.48 μm with a pump power of 7W.

Quasi-phase matching in periodic nonlinear structures provides an efficient method to phase match a single nonlinear process. However, periodic modulation is not suitable for multiple-wavelength interactions, such as dual wavelength second harmonic generation, frequency tripling and frequency quadrupling. Multiple processes may be phase-matched by using aperiodic, rather than periodic, modulation of the nonlinear coefficient. We have developed a method to phase match any two arbitrary processes by quasi-periodic modulation of the nonlinear coefficient. This method was experimentally verified by performing dual wavelength second harmonic generation, as well as frequency tripling (based on simultaneous phase matching of frequency doubling, followed by sum frequency generation of the first and second harmonic waves) in a single quasi-periodically-poled KTP crystal. Additional degrees of freedom are obtained by using two dimensional periodic or quasi-periodic modulation of the nonlinear coefficient. We discuss frequency tripling by a 2D periodic structure, as well as the application of 2D quasi-periodic structures for nonlinear frequency conversion.

Near stoichiometric LiTaO₃ is investigated for high power quasi-phase-matched optical frequency conversion applications due to its high optical damage threshold and low coercive field. In this work, near stoichiometric undoped and MgO-doped LiTaO₃ wafers were characterized by transmission through cross-polarizes, x-ray diffraction and microscope inspection. Periodically inverted domain structures were fabricated in 1 to 4mm thick wafers, by electric field poling in vacuum. Efficiency values between 10% and 16% were obtained for direct frequency conversion of 1 μm to 4 μm light using optical parametric oscillations scheme. The resulting periodically poled structure quality and frequency conversion efficiency seems to be limited by crystalline imperfections of the wafers.

The introduction of periodically poled crystals with high non-linear coefficients has lowered significantly the threshold for parametric processes. This progress enables pumping frequency conversion devices with low pulse energy, Q-switched, diode-pumped, solid-state lasers. New non-linear optical ferroelectric materials, such as KTP and Stoichiometric Lithium Tantalate (SLT) were proven to exhibit adequate d_eff, higher optical damage resistance and lower photo-refractivity in comparison to well-known periodically poled Lithium Niobate. Advances in poling technology have enabled the production of relatively thick periodically poled crystals from those materials. Thus, in principal much higher average power levels can be converted. We have investigated the effects that limit frequency conversion efficiency as power levels are increased. Average power induced thermal lensing and thermal phase mismatching were considered. The resulting power limitations are discussed, and under some assumptions quantitative expressions for these limits were formulated. Thermal lensing imposes a limit on the local power density. Thermal phase mismatching imposes a limit on the overall power.

We introduce the results of the study of intracavity quasi-phase-matched three-frequency wave interactions in active nonlinear periodically poled crystals. The process of self-frequency summing in periodically poled Nd:Mg:LiNbO₃ has been studied. Quasi-phase-matched sum-frequency generation at 0.464 μm by self-frequency summing of fundamental radiation at 1.084 μm and unabsorbed part of pump radiation of diode laser at 0.810 μm in periodically poled Nd:Mg:LiNbO₃ crystal has been realized experimentally.

SNLO is free, public domain software developed at Sandia National Laboratories. It is intended to assist you in selecting the best nonlinear crystal for your particular application and to predict its performance. This paper briefly describes its functions and how to use them.

We present a theoretical and experimental investigation of the efficiency, beam quality and signal bandwidth of a confocal, unstable OPO resonator. Reduction by more than 20 times of the divergence as well as bandwidth narrowing by factor of ~5 of the signal beam, in comparison to the plane-parallel resonator, are obtained. Resonator configurations have been found where the beam quality of the signal exceeds the beam quality of the pump.

A method is presented here to determine the dependence of both the threshold and the conversion efficiency of a singly resonant optical parametric oscillator on the focusing conditions of the pump and signal beams, phase mismatch and incident pump power. Strong pump depletion effect is included.

A tandem PPLN and ZGP optical parametric oscillator (OPO) has demonstrated the generation of multiple wavelength output in the mid-infrared. A pulsed Nd:YVO₄ laser, oeprating at 1.342 microns, pumped a PPLN OPO that generated 2.12 microns and 3.66 microns. 8.4W of 1.342 microns was available at the PPLN. The PPLN OPO produced 2.6W at 2.12 microns, of which 2.35W was available to pump the ZGP OPO. The ZGP OPO generated a total combined output of 0.85W at 3.9 microns and 4.6 microns. The threshold of the ZGP OPO was measured to be 60 micro-Joules (10.6 MW/cm², ~18 ns FWHM pulse).

Single frequency laser sources, which also provide tunability, have wide use in spectroscopy and remote sensing as well as for other applications such as optical pumping. Optical parametric oscillators (OPOs) offer the potential for broadly tunable output in spectral regions inaccessible by conventional laser sources. We report here on the design and use ot an OPO architecture developed to produce pulsed, tunable, single-frequency output in the mid-infrared spectral region and used for optical pumping of gas. Design information about two separate OPOs that were developed will be presented along with experimental details of the optical pumping of CO on the (3-0) band around 1.57 μm and on the (2-0) band around 2.3 μm.

We have experimentally demonstrated the existence of super-broadband non-degenerated phase matching for a signal with a wavelength of 911 nm in KD*P crystal pumped with wavelength of 527nm. Parametric amplification coefficient of more than 10⁷ in three cascades is achieved. This resulted in pulse energy 10mJ at the output of third cascade. It is shown that in the KD*P crystal chirped pulses of conventional femtosecond sources (a Ti:Sa laser at 911 nm and a Cr:forsterite laser at 1250 nm) can be amplified up to the level that ensures multipetawatt power after compression.

We describe the properties of novel blue-green sources based on intracavity frequency doubling of the Novalux family of high-brightness infrared surface-emitting lasers. They are highly compact, efficient, reliable, stable and manufacturable, capable of emitting over 40-mW cw power at 488 nm and other custom wavelengths in the range 460-532 nm with single frequency and single-spatial mode.

ZnO nanocrystalline thin layers are of growing interest for ultrafast optical applications. Previous investigations delivered different values of second order susceptibilities. The quantitative contribution of grain structure - depending on fabrication procedure - is not well understood. For our investigations, pure and doped polycrystalline and amorphous ZnO thin filmes of 0.1 to 1.5 μm thickness have been prepared by spray pyrolysis and alternative techniques. Texture, thickness and further structural properties of the layer have been characterized by SEM, AFM, XRD, and optical spectroscopy. Using 20-fs Ti:Sa laser pulses centered at 800 nm, we measured the angular dependence of SHG intensity and determined second order susceptibilities. For a small range of crystallinity parameters, pronouced SHG efficiencies appear. From our experiments, design parameters for ZnO nanolayers can be derived which enable a tailoring of sandwich structures for advanced non-linear processing and femtosecond laser autocorrelation.

We report on two-photon pumped frequency upconverted emission in doped PMMA fibers. The PMMA fibers were doped with a novel organic chromophore 1,4-bis(4-diphenylamino-styryl)-benzene (referred to as SP35) which is designed specifically to emit in the blue spectral region. Strong upconverted blue emission was observed in the fibers when longitudinally pumped at 800nm with a Titanium Sapphire laser. We measured a large two-photon absorption cross section for SP35 of 7.8 x 10^-19cm⁴/GW using the non-linear transmission method. Our study shows that a well designed organic chromophore in combination with a suitable fiber geometry makes this system appealing for the development of an upconversion blue laser source.

A wide range of physical properties of mercury thiogallate crystals is studied for development and optimization of OPO based on these crystals. The obtained results provide to conclude that OPO on HgGa₂S₄ crystals can occupy one of the leading positions among the analogous devices in the mid-infrared region.

The propagation of high power narrowband laser pulses in multimode fibers and the limitations due to SBS are presented. An injection seeded pulsed Nd:YAG laser operating at 10 Hz was used to pump undoped step index fibers to determine the SBS threshold under various conditions. Measurements on 50μm core diameter fibers with various fiber lengths and pulse durations at 1064 nm were performed and simulated with a computer code. The code considers the time dependent coupling between the pump wave, the Stokes wave, and the acoustic wave. The experimental results are in good agreement with the numerical predictions. Our results quantify the limitations of high power narrowband pulse transmission in multimode fibers.

A new phase conjugate mirror based on stimulated Brillouin scattering (SBS) in a multimode fiber amplifier is presented. The optical amplification leads to a drastic reduction of the SBS threshold. A peak power threshold of 5 W was detected for a 10 m long Ytterbium doped fiber amplifier. The experimental examinations include the measurements of the phase conjugate fidelity, the temporal behavior of the Stokes pulse and the spectra of the back scattered light.

When a Kerr medium is pumped by a strong laser beam, the nonlinear process of four-wave mixing (FWM) can mix the pump laser and a weak signal to generate a phase-conjugated version of the signal. Optical phase conjugation (OPC) may be employed to compensate the chromatic dispersion and nonlinearity of transmission fibers. It may even serve as a parametric amplifier when the pump is sufficiently intense. Furthermore, the FWM effect is capable of phase-conjugating or amplifying many wavelength-division multiplexed (WDM) signals simultaneously. However, the same FWM effect results in parasitic processes by generating inter-mixing terms among the WDM signals. The center frequency of such unwanted mixing terms may coincide with some of the original or conjugated WDM signals to cause significant interference. This paper studies such interference effect by means of theoretical calculation and computer simulation. It is shown that the coherent interference effect decreases as the pump-power to signal-power ratio (PSR) increases. Unfortunately, there could still be strong interference even with a PSR of 20dB. Some guard-band in the frequency domain is necessary to avoid such coherent interference: if the total bandwidth of the WDM signals is W, then the nearest signal should be more than W away from the pump frequency.

The impact of nonlinear optical effects, the optimization of the dispersion, the bandwidth of the filters and the optical signal powers play a major role in an optical network and even more the higher the data rates are. This work deals with the simulation of dispersion in order to determine its impact on the performance of high-capacity WDM-transmission systems. By consideration of nonlinear optical effects and suitable dispersion management, it is shown that the system performance can partly be improved. A 10 Gbps or 40 Gbps external modulated laser signal is transmitted through a standard single mode fiber (SSMF) followed by a dispersion compensation fiber (DCF) (postcompensation). Due to cross-phase modulation, four-wave mixing and self-phase modulation crosstalk which influences the optimum length of the DCF can be detected. The filter bandwidth and length of the DCF have been optimized for various signal powers and two different data-rates. It turned out that the influence of different non-linear effects on the system performance can be partly reduced by optimized dispersion management (undercompensation). It is shown that the optimum length of the DCF is independent of the signal bandwidth. The simulation reasons the maximum launched power per channel and the optimum filter bandwidth for 40 Gbps transmission systems. Real measurements on optical components and networks agree with our simulation results.

We theoretically investigate in the aberrationless approximation the self-action of the elliptically polarized Gaussian pulse during its propagation in a thin dish with a nematic liquid crystal in the isotropic phase. Quadrature formulas are obtained to describe the time history of the intensity, the elliptisity degree and the rotation angle of the polarization ellipse of the output radiation at the different points of the beam cross-section. They are expressed in terms of the parameters describing two, essential near the temperature of the isotropic-nematic phase transition, mechanisms of the spatial nonlocality of the nonlinear medium optical response, and in terms of the other parameters, which describe the nematic liquid crystal and the elliptically polarized incident pulse. The former mechanism is specified by the medium heating due to light absorption; the latter is determined by the fluctuations of the nematic liquid crystal order parameter tensor near the temperature of the isotropic-nematic phase transition. It is shown that for some values of temperature and of the nematic liquid crystal parameters the elliptical polarization of the incident pulse, which is constant at the entry of the thin dish, transforms into the linear or another different elliptical one at the exit and keeps this new state up to the pulse tail. The dependence of the ellipticity degree on time becomes significantly nonmonotonic and changes its sign in some cases. The nonlocality of the nonlinear medium optical response weakens these transformations.

The measurements of nonlinear refractive indices and third-order susceptibilities responsible for self-action effects in nonlinear-optical crystals (KDP, KTP, BBO, LiNbO3) in various spectral ranges (1064 and 532 nm) were carried out by the Z-scan method. It was obtained that investigated media (excepting KTP crystal λ=1064 nm) had self-focusing properties. The significant values of nonlinear losses were recorded at λ=532 nm. The analysis and comparison of experimentally and theoretically obtained values of nonlinear susceptibilities are given. The angular and polarization dependencies of Kerr nonlinearities were analyzed.

We report a high-power, kilohertz, ultrafast optical parametric amplifier (OPA) that is seeded by white-light continuum and contains three amplification stages. Two 3-mm KTA crystals cut in type-II phase-matching configuration are used in the OPA system which is capable of producing up to 70 μJ, 140 fs infrared laser pulses at wavelength ranging from 2.9 to 4 μm. A full-scaled numerical simulation on the OPA system was performed. Actual white-light seeded signal pulse and finite phase-matching bandwidth were taken into account in the calculation. Material dispersion and linear absorption of all the optical components involved were properly incorporated. The simulation results match the experimental results almost perfectly. Our simulation provides an essential tool to design and optimize the OPA systems. A step-by-step design procedure based on this simulation algorithm is presented.

We present the results of investigation of the conditions of growing crystals of solid solutions AgGa_1-xIn_xSe₂ of high optical quality for noncritical phase matching processes. The obtained crystals are characterized by low absorption coefficient (0.002 cm^-1) and high efficiency of conversion of pumping radiation into second harmonic.