This PDF file contains the front matter associated with SPIE Proceedings Volume 6875, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Using Fresnel phase retrieval method for two intensity profiles, we first construct the phase-map of the HeNe laser beam in a specially built optical system. After validating this result with the analytical value we proceeded to the nonlinear three-wave interaction. The Fresnel technique is once again employed to obtain the phase map of the input pump and signal beam. The phase information of these input beams are then used in a two-dimensional numerical model we have developed for three-wave nonlinear interactions. The outcome from the numerical model is then compared to the phase map of the output pump and signal beam.

Near-stoichiometric lithium tantalate (SLT) crystals were produced from congruent lithium tantalate by a vapor-transport equilibration (VTE) process. The VTE'ed SLT (VSLT) crystals exhibited very low coercive field of 60-120-V/mm and improved high intensity damage resistance. The ~603°C Curie temperature of the congruent raw material climbed to 693±0.1°C in the VSLT crystal regardless of the congruent crystal stoichiometric composition or of the exact VTE process temperature profile. Stable, high power near room temperature second harmonic generation (SHG) and optical parametric oscillation (OPO) were demonstrated with these crystals. SHG measurements of a 1064-nm pulsed laser were realized by an 8-μm period grating, 21-mm-long sample. With 29-ns long pulses at 20-kHz repetition rate, 7.3-W (average power), of 532-nm radiation was generated with 55% conversion efficiency. With 25-ns long pulses at 10-kHz repetition rate in the same sample, 6.3-W of average-power with 61% conversion efficiency was obtained. 1.41-W average-power, at 4.013-μm idler wavelength was generated in an OPO configuration. The 28.65-μm period grating, 24-mm-long sample, was pumped by 25-ns pulses, 10-kHz repetition rate, 1.064-μm Nd:YVO₄ laser. In addition to the original (intended) signal and idler wavelengths, 0.27-W was obtained at 4.686-μm idler wavelength, by a secondary OPO process which developed in the system. Primary and secondary OPO operation was also observed in a 27.15-μm period grating, 38-mm-long sample. 0.67-W at 4.48-μm and 0.15-W at 5.03-μm were generated in this experiment.

We present design, fabrication and characterization of a novel integrated device for tuning the wavelength of quasi-phase matched (QPM) second harmonic generation (SHG) in a periodically poled lithium niobate (PPLN) wavelength converter. A Cr/Pt/Au thin film layer is deposited on a PPLN device with a polymer buffer layer to work as a micro-heater. Wavelength tuning is achieved by applying current to the micro-heater, which changes the effective period of QPM grating and thus the QPM wavelength through the thermal optics effect (TOE). In contrast to the conventional temperature tuning method based on a bulky oven, the proposed device has excellent characteristics such as compact, fast tuning speed and low power consumption.

We report a ZGP OPO/OPA system capable of producing >30 mJ at a signal wavelength of 3.4 μm. Our pump source for the OPO/OPA is a 2.05-μm, diffraction-limited Ho:YLF master-oscillator power-amplifier (MOPA) producing ~150 mJ energy per pulse at repetition rate from single shot to ~500 Hz (>100 mJ at 1 kHz). The Ho-MOPA output was split ~2:1 into two beams: one (~50 mJ per pulse) pumping an image-rotating RISTRA ZGP OPO to generate a 3.4-μm signal wave with >10 mJ of pulse energy and near diffraction-limited beam quality, and the other to pump a ZGP OPA stage to increase the signal wave to ~30 mJ per pulse.

In this work we present the development of the sub-micron ferroelectric domain structuring technology in KTiOPO₄. We used these structures to demonstrate second-order interactions involving counter-propagating waves. Of special interest is the mirrorless optical parametric oscillator, where distributed feedback between the counter-propagating signal and idler waves obviates the need for mirrors, surface coatings or precise cavity alignment. Mirrorless optical parametric oscillator also demonstrates some unique and useful spectral properties. These experimental demonstrations are but first steps towards a number of tantalizing applications which, however, require even smaller ferroelectric domain periodicities and further work on the material structuring technology.

We present a systematic study of the birefringence (including Sellmeier equations valid in the 0.6-11.5 μm range) and nonlinearity of the orthorhombic AgGaGe_nSe_2(n+1) crystals for n=2...5, solid solutions in the system AgGaSe₂-nGeSe₂. The birefringence, e.g. n_a-n_c at 1064.2 nm, increases from 0.114 for n=2 (AgGaGe₂Se₆) to 0.149 for n=5 (AgGaGe₅Se₁₂) which substantially exceeds the birefringence of the uniaxial AgGaSe₂ (~0.022), the parent compound in the limit n=0. All four quaternary compounds are optically negative biaxial crystals. The calculated SHG limit (minimum fundamental wavelength) is ≈1470 nm for AgGaGe₂Se₆ and ≈1240 nm for AgGaGe₅Se₁₂, for type-I interaction and propagation along the Y principal optical axis. These limits are much lower than the ≈3120 nm limit for type-I interaction in AgGaSe₂. Thus, the AgGaGe_nSe_2(n+1) crystals can be used for SHG down to their band-edge. The results for the nonlinear coefficients of AgGaGe_nSe_2(n+1) (n=3, 4 and 5), obtained from phase-matched SHG, indicate weak dependence on the composition. On the average, the larger nonlinear coefficient d₃₁ is very close to d₃₆ of AgGaSe₂ (~30 pm/V) while d₃₂ is roughly two times smaller.

We developed a source of terahertz-frequency radiation using intracavity difference-frequency mixing in three types of micro-structured GaAs between the signal and idler waves of a doubly resonant synchronously pumped optical parametric oscillator (DRO). The pump, signal, and idler waves were type-II quasi-phase-matched (QPM) by a 10-mm-long magnesium-doped periodically poled LiNbO₃ crystal. The oscillator operated near frequency degeneracy with signal and idler bandwidths of 100-200 GHz. The DRO was pumped by a CW-mode-locked laser with a 1064-nm wavelength, 7-ps pulse width, 50-MHz repetition rate, and average power of 10 W. The cavity round-trip power losses were 4-5% for each wave, and at the largest pump power as much as 120 W of total signal and idler average power was stored inside the cavity. We developed an electronic locking feedback network that provided >15 minutes of stable DRO operation with over 100 W of intracavity average power and power fluctuations of 5-10%. The signal and idler pulse widths were characterized with an extracavity sum-frequency generation process between the pump and resonant OPO pulses. We developed a split-step Fourier propagator to model the temporal properties of the signal and idler pulses, and we found excellent agreement with experimental results.

Widely tunable terahertz (THz) -wave generation using difference frequency generation (DFG) in an organic N-Benzyl-2-methyl-4-nitroaniline (BNA) crystal was demonstrated. An organic nonlinear optical (NLO) BNA crystal is one of the promising materials for efficient and strong THz-wave generation because of its potential to have a sufficiently large enough second-order optical nonlinearity. Large and high quality single crystals of BNA (Φ8×30mm) were successfully grown by a vertical Bridgman method. The NLO coefficient d₃₃ of BNA crystal is about 230pm/V. It is the largest value reported for any yellow-colored NLO materials. BNA has low refractive index dispersion between the optical and THz-wave region, therefore the colinear phase matching condition of the Type0 configuration is satisfied by using 0.7~1μm band pump wavelength. So, we developed a near-infrared dual-wavelength pump source for BNA-DFG. Two KTiOPO₄ (KTP) crystals were mounted on galvano scanners inside a double-pass optical parametric oscillator (OPO). It is pumped using a frequency-doubled Nd:YAG laser (532 nm, 8 ns, 100 Hz). The signal wave of the KTP-OPO output was controlled independently and rapidly using a galvano scanner. We successfully generated THz-wave using organic BNA crystal. The THz-wave generation range is from 0.1 to 15THz, while the pumping dual-wavelength is controlled in the 0.8-0.9μm range.

Orientation-patterned GaAs (OPGaAs) shows great promise as a nonlinear optical material for frequency conversion in the 2-5 μm and 8-12 μm regions. We report recent progress in each of the three main areas of OPGaAs development: fabrication of patterned templates using a combination of wafer bonding and MBE techniques; thick-layer HVPE growth; and material and OPO device characterization. This work has led to significant improvements in material quality, specifically reduced optical loss, increased sample thickness, improved patterned domain fidelity, and greater material uniformity. Advances in material quality have in turn enabled demonstration of OPO devices operating in the 3-5 μm spectral region. Optical loss and OPO performance measurements on a series of OPGaAs samples are presented, with the goal of understanding how these properties are influenced by growth conditions, and how OPO performance may be improved. Research continues on understanding loss mechanisms, correlating performance with material properties, transitioning the technology into an industrial process, and extending it to additional materials.

Zincblende semiconductors, such as GaAs, GaP and others, show great potential for quasi-phase-matched nonlinear optical frequency conversion. In addition to broad infrared transparency and high nonlinear coefficient of zincblende materials, the symmetry of their nonlinear optical tensor allows operating nonlinear-optical devices with the following unusual features: second harmonic generators which are not sensitive to the direction of linear polarization, optical parametric oscillators which can be pumped by circular and even random polarization, and optical parametric amplifiers of randomly-polarized radiation.

Material preparation methods and device fabrication technologies for realization of low loss periodically oriented GaAs waveguides are reported. Planar waveguide structures were grown by MOCVD on periodically patterned templates prepared by wafer bonding and selective layer removal. Ridge waveguides were designed and fabricated from the planar structures with emphasis on waveguide loss minimization. Record low losses of 2.0db/cm in periodically oriented waveguides and 0.95db/cm in single domain waveguides were measured. Routes for further loss reduction in patterned GaAs waveguides are discussed and initial results from further work to reduce waveguide corrugation are presented.

Nonlinear optical materials play a key role in the development of coherent sources of radiation as they permit the frequency conversion of mature solid-state lasers into spectral ranges where lasers do not exist or perform poorly. The availability of efficient quasi-phasematched infrared materials is thus considered as important for the development of several optronics applications. This paper will review the recent progresses achieved with thick Orientation-Patterned GaAs structures. We will present results obtained in growing a 500 μm thick layer on 2 cm long structures with low optical losses (less than 0.02 cm^-1). This loss coefficient is low enough to allow the operation of a highly efficient GaAs OPO in the Mid-IR range.

The fabrication of thick orientation-patterned GaAs (OP-GaAs) films is reported using a two-step process where an OP-GaAs template with the desired crystal domain pattern was prepared by wafer fusion bonding and then a thick film was grown over the template by low pressure hydride vapor phase epitaxy (HVPE). The OP template was fabricated using molecular beam epitaxy (MBE) followed by thermocompression wafer fusion, substrate removal, and lithographic patterning. On-axis (100) GaAs substrates were utilized for fabricating the template. An approximately 350 μm thick OP-GaAs film was grown on the template at an average rate of ~70 μm/hr by HVPE. The antiphase domain boundaries were observed to propagate vertically and with no defects visible by Nomarski microscopy in stain-etched cross sections. The optical loss at ~2 μm wavelength over an 8 mm long OP-GaAs grating was measured to be no more than that of the semi-insulating GaAs substrate. This template fabrication process can provide more flexibility in arranging the orientation of the crystal domains compared to the Ge growth process and is scalable to quasi-phase-matching (QPM) devices operating from the IR to terahertz frequencies utilizing existing industrial foundries.

Orientation-patterned zinc selenide (OPZnSe) is a unique quasi-phase-matched nonlinear optical material for enabling frequency conversion from visible to long-wave infrared wavelengths. We have fabricated and tested OPZnSe devices over a wide spectral range. Single crystal OPZnSe films of greater than 1 mm thickness were grown and characterized for optical loss showing an attenuation coefficient less than 0.05 cm^-1 from 1 to 12 μm. We demonstrated nonlinear frequency conversion in the near infrared, mid-infrared, and long-wave infrared in these devices through a variety of nonlinear mixing processes.

Tunable, mid-infrared lasers based on quasi-phase matched bulk PPLN crystals have successfully been implemented on airborne atmospheric research platforms and enabling a detectable fractional absorbance of about 5E-7, which equates to single digit part-per-trillion detectable concentrations for many atmospherically important trace gases. Emerging development of ridge waveguide type PPLN crystals show promising performance characteristics, including 100 times better conversion efficiency and good beam quality, which enable more compact system designs. In addition, the flexibility afforded by QPM structured materials to generate coherent mid-infrared radiation, permit unique multi-wavelength operation and detection techniques.

Recent EPA regulations targeting mercury (Hg) emissions from utility coal boilers have prompted increased activity in the development of reliable chemical sensors for monitoring Hg emissions with high sensitivity, high specificity, and fast time response. We are developing a portable, laser-based instrument for real-time, stand-off detection of Hg emissions that involves exciting the Hg (6 ³P₁ ←6 ¹S₀) transition at 253.7 nm and detecting the resulting resonant emission from Hg (6 ³P₁). The laser for this approach must be tunable over the Hg absorption line at 253.7 nm, while system performance modeling has indicated a desired output pulse energy ≥0.1 μJ and linewidth ≤5 GHz (full width at half-maximum, FWHM). In addition, the laser must have the requisite physical characteristics for use in coal-fired power plants. To meet these criteria, we are pursing a multistage frequency-conversion scheme involving an optical parametric amplifier (OPA). The OPA is pumped by the frequency-doubled output of a passively Q-switched, monolithic Nd:YAG micro-laser operating at 10-Hz repetition rate and is seeded by a 761-nm, cw distributed-feedback diode laser. The resultant pulse-amplified seed beam is frequency tripled in two nonlinear frequency-conversion steps to generate 253.7-nm light. The laser system is mounted on a 45.7 cm × 30.5 cm breadboard and can be further condensed using custom optical mounts. Based on simulations of the nonlinear frequency-conversion processes and current results, we expect this laser architecture to exceed the desired pulse energy. Moreover, this approach provides a compact, all-solid- state source of tunable, narrow-linewidth visible and ultraviolet radiation, which is required for many chemical sensing applications.

We report a compact high-power continuous-wave green laser for a scanning laser projector using one-dimensional diffractive spatial modulators (GxL modulators). The green laser oscillates in one-dimensional multi-transversal modes and generates a beam in a line from a periodically-poled stoichiometric lithium tantalate (PPSLT) crystal inside the laser cavity. The line beam enables diffraction-limited focusing in one direction and can be easily transformed into a top-hat beam because of the low spatial coherency in the multi-transversal-mode direction. The maximum output green power is 7.2W when pumped at a LD current of 24 A. The input electrical-power efficiency to the green output is as high as 16% at 6W green power output. We used the laser to build compact, air-cooled laser modules with a cavity footprint as small as 50 mm². The laser showed no degradation over 8,500 hours at 3W output.

A compact pulsed RGB laser source based on periodically-poled MgO doped SLT pumped at 532 nm is reported. The operation of the source at near-room temperature and at high temperature is evaluated for optimal performance.

We demonstrate cladding mode assisted supercontinuum generation in a solid core photonic crystal fiber. Although the fiber is commonly considered as endlessly single mode, we show that coupling light into the cladding excites much broader spectrum compared with the situation when only fundamental mode is excited. Comparing experimental data with the results of the modal analysis and the simulations of the pulse propagation in the fiber, we conclude that cladding mode has more favorable dispersion characteristics for the continuum generation. We discuss possible usage of the cladding mode assisted supercontinuum in biosensor applications.

The possibility of influencing resonance energy transfer through the input of off-resonant pulses of laser radiation is the subject of recent research. Attention is now focused on systems in which resonance energy transfer is designedly precluded by geometric configuration. Here, through an optically nonlinear mechanism - optically controlled resonance energy transfer - the throughput of non-resonant pulses can facilitate energy transfer that is, in their absence, completely forbidden. The system thus functions as an optical buffer, with excitation throughput switched on by the secondary beam. For applications, a system based on two parallel nano-arrays is envisaged. This paper will establish and discuss the principles - those that can be exploited to enhance switching characteristics and efficiency, and others (such as off-axis excitation transfer) that may represent cross-talk limitations. Principles to be explored in detail are the interplay between geometric features, including the array architecture and repeat distance (lattice constant), the array spacing and translational symmetry, the orientations of the transition dipoles, and the magnitude of the relevant components of the nonlinear response tensors. The aim is, through a determination of key parameters, to inform a program of optimization that can deliver specific criteria for realizing the most efficient systems for implementation.

An opportunity of shaping three-wave solitary coupled states within the co-directional collinear acousto-optical interaction between two optical waves and the suffering losses acoustic pulses in a square-law nonlinear crystal. The considered analytical model for this process with the mismatched wave numbers describes a regime of strongly coupled modes. They are studied using the first order approximations relative to a pair of the parameter of smallness. We assume that both the acoustic losses and the wave number mismatch represent these pair of the smallness parameters of the same order. Three-wave collinear acousto-optical coupled states originating within such an interaction exhibit an asymmetry in shapes of their envelopes and shifts of extrema in their intensity distributions.

There has recently been a great deal of interest in searching for new vitreous materials for application as hosts in infrared-to-visible light upconverters or optical amplifiers based upon rare-earth doped systems. Some of their many applications include: color displays, high density optical recording, biomedical diagnostics, infrared laser viewers and indicators, fiber lasers and amplifiers. Fluorophosphate-based glasses have recently emerged as auspicious candidates for such photonic devices applications. These glasses are advantageous because they present low nonlinear refractive indeces, better mechanical strength, chemical durability, and thermal stability than fluoride-based glasses and are suitable for developing low-loss, high strength, and low-cost optical fibers. It has recently been shown also that the fluorophosphate-based glass is an excellent candidate for high power lasers and broadband amplifiers in the eye-safe region around 1.5 μm for applications in communication, medicine, and meteorology. The present work involves the investigation of optical transitions and upconversion fluorescence spectroscopy of trivalent lanthanide ions Er3+ and Tm3+ codoped with Yb3+ in P2O5-PbO-MgF2 glass, excited with near-infrared diode lasers. The dependence of the upconversion luminescence upon the Yb3+-concentration and diode laser power, and the upconversion excitation mechanisms involved are also investigated. The viability of using these glasses as host for practical applications in optical temperature sensors will also be presented.

Irradiance scan measurements of the nonlinear absorption and refraction coefficients of CdTe were performed at room temperature and at 77 K and compared to the values obtained in previous experiments using a different technique.

The present paper analyses features of super-continuum generated from pulsed and CW excitation. It has been shown that generation mechanisms and many properties of super-continuum produced with CW excitation are cardinally different from those of super-continuum generated by pulsed excitation. On the other hand, different applications pose different, and often opposite requirements to the super-continuum, which cannot be satisfied within a single universal technique of super-continuum generation. In this connection, we have analyzed pulsed and CW schemes of super-continuum generators and conditions which should be fulfilled in order to achieve optimal super-continuum parameters required in most typical super-continuum applications (metrology, tomography, spectroscopy, communications). In particular, we consider a special regime of super-continuum generation, where an amplitude-modulated CW pump breaks up into periodic sequence of ultra-short pulses under the action of induced modulation instability. In the work we have studied for the first time the effect of noise (spontaneous emission) on this break-up and determined conditions for depth and frequency of initial modulation needed for this process both numerically and analytically (in the approximation of slightly intensity modulated CW pump radiation).

BiB₃O₆ (BIBO), the first low-symmetry (monoclinic class 2) inorganic nonlinear crystal that became commercially available, possesses some unique advantages for applications in ultrafast laser technology which are primarily related to its dispersive properties. In the present paper, these properties are analyzed in more detail and compared with other crystals. Of special interest is the pumping of this material near 800 nm for broadband parametric amplification in the near-infrared between 1.15 and 2.4 μm. We present experimental results on generation and amplification of ultrabroadband femtosecond continua in this spectral range using amplified Ti:sapphire lasers as pump sources.

We observe a photosensitivity apparently different from that associated with fiber grating inscription in a supercontinuum-generating germanosilicate fiber. Transmission of intense femtosecond ~800 nm pulses in the heavily Ge-doped fiber progressively produces a waveguide at the entrance of the fiber. The waveguide behaves as a multi-millimeter long fiber bandpass filter which scatters away light with wavelength shorter or longer than 850 nm. This photosensitivity is therefore termed as the photoscattering effect. A model incorporating color center formation is proposed to explain the underlying mechanism. A 5-photon absorption process likely serves as the common origin of this effect and the ~800 nm photosensitivity producing low-loss waveguides in bulk silica glass and Type I-IR fiber Bragg gratings in side written optical fibers.

Three conditions for non-collinear third harmonic generation by a PTR glass volume Bragg grating are demonstrated using infrared femtosecond pulse illumination. Each condition corresponds to a different angle of grating orientation. We identify the angles as corresponding to Bragg diffraction at ω, Bragg diffraction at 3ω, and a non resonant Bragg angle involving three ω photons interacting with a nonlinear grating vector. The generation of non-collinear third harmonic at each of these angles is modeled with wavevector interactions. Theoretical predictions from the wavevector equations are obtained and compared to experimental measurements. We discuss the nonlinear grating in the PTR glass grating as resulting from modulation in the nonlinear refractive index of PTR glass.

We report the operation of passively Q-switched diode-end-pumped Nd:YAG and Nd:YVO4 lasers by employing Cr⁴⁺-doped garnets with Ca²⁺ or Mg²⁺ as charge compensators. We found that the laser performance improved significantly, mainly in the Nd:YVO₄ system when (Cr⁴⁺,Mg²⁺):YAG sample was used as a passive Q-switching. For example, in the Nd:YVO₄ and Nd:YAG lasers, the maximum peak power using (Cr⁴⁺,Mg²⁺):YAG saturable absorber was higher by a factor of 8.5 and 2.6, respectively, relative to (Cr⁴⁺,Ca²⁺):YAG. This fact is attributed to better optical quality of the (Cr⁴⁺,Mg²⁺):YAG sample, as a result of improved dopant distribution and reduced internal stresses inside the saturable absorber crystals. Similar passively Q-switched laser performance can be obtained by using other garnets with an open structure, and hence, with low internal stresses, such as (Cr ⁴⁺,Ca²⁺):GGG. We also compared the laser performance of Nd:GdVO₄ with the same saturable absorbers and obtained both passive Q-switching and passive mode locking. By using an analytical model with the relevant physical parameters of the laser crystals and saturable absorbers it is possible to optimize the laser performance.

We present a generic approach for efficient generation of CW light with a predetermined wavelength within the visible or UV spectrum. Based on sum-frequency generation (SFG), the circulating intra-cavity field of a high-finesse diode pumped CW solid-state laser (DPSSL) and the output from a tapered, single-frequency external cavity diode laser (ECDL) are mixed inside a 10 mm periodically poled KTP crstal (pp-KTP). The pp-KTP is situated inside the DPSSL cavity to enhance conversion efficiency of the nonlinear mixing process. This approach combines different solid state technologies; the tuneability of ECDLs, the high intra-cavity filed of DPSSLs and flexible quasi phase matching in pp-tapered ECDL with a center wavelength of 766 nm in combination with a high finesse Nd:YVo4 laser at 1342 nm. Up to 308 mW of light at 488nm was measured in our experiments. The conversion of te ECDL beam was up to 47% after it was transmitted through a PM fiber, and up to 32% without fiber coupling. Replacing the seed laser and the nonlinear crystal makes it possible to generate light at virtually any desired wavelength withing the visible spectrum.

Cooperative energy-transfer upconversion luminescence in Tb³⁺/Yb³⁺-codoped PbGeO₃PbF₂-CdF₂ vitroceramic and its precursor glass under resonant and off-resonance infrared excitation, is investigated. Bright UV-visible emission signals around 384, 415, 438 nm, and 473-490, 545, 587, and 623 nm, identified as due to the ⁵D₃(⁵G₆) → ⁷F_J(J=6,5,4) and ⁵D₄→⁷F_J(J=6,5,4,3) transitions, respectively, were readily observed. The results indicate that cooperative energy-transfer between ytterbium and terbium ions followed by excited-state absorption are the dominant upconversion excitation mechanisms herein involved. The comparison of the upconversion process in a vitroceramic sample and its glassy precursor revealed that the former present much higher upconversion efficiency. The dependence of the upconversion emission upon pump power, temperature, and doping content is also examined.

Results for a new compact 488 nm solid-state laser for biomedical applications are presented. The architecture is based on a multi-longitudinal mode external cavity semiconductor laser with frequency doubling in a ridge waveguide fabricated in periodically poled MgO:LiNbO₃. The diode and the waveguide packaging have been leveraged from telecom packaging technologies. This design enables built-in control electronics, low power consumption (≤ 2.5 W) and a footprint as small as 12.5 x 7 cm. Due to its fiber-based architecture, the laser has excellent beam quality, M² <1.1. The laser is designed to enable two light delivery options: free-space and true fiber delivered output. Multi-longitudinal mode operation and external doubling provide several advantages like low noise, internal modulation over a broad frequency range and variable output power. Current designs provide an output power of 20 mW, but laser has potential for higher power output.

Green-induced infrared absorption (GRIIRA) properties were characterized for LiNbO₃ (LN) and LiTaO₃ (LT) single crystals. GRIIRA was measured using a photothermal common-path interferometer. Several LN and LT with different concentrations and doping materials were investigated. Mg-doped near-stoichiometric LT (Mg-SLT) had the lowest IR absorption. In addition, no GRIIRA was observed only in MgSLT. Therefore, Mg-SLT could be the most suitable material for high power green generation. In LN crystals, higher GRIIRA was observed in non-doped congruent LN (CLN) which has low photorefractive damage threshold. The 1.3 mol% Mg doped SLN had the lowest GRIIRA within the investigated LN crystals. Even in the materials with low GRIIRA, two different characteristics were observed; initially high IR absorption and slow relaxation time of GRIIRA. The first characteristic was observed for Mg doped LN which has a higher number of scattering centers. The second was strongly observed in Mg doped LN which has a higher level of absorption in the UV region.

90° phase-matched type-I second harmonic generation (SHG) of CO₂ laser radiation at 10.591μm is demonstrated at 203°C in mixed chalcopyrite AgGa_1-xIn_xS₂ crystal with x = 0.14 ± 0.01. In addition, temperature-tuned difference frequency generation (DFG) at 4.02μm is obtained by mixing the idler output of a Nd:YAG third harmonic pumped β-BBO optical parametric oscillator and its fundamental source at 1.0642μm. The Sellmeier and thermo-optic dispersion formulas that reproduce well these experimental results are presented.

The 90° phase-matched direct type-1 and type-2 third-harmonic generation (THG) at 0.3263 and 0.3837 μm were observed along x of the monoclinic BiB₃O₆ at room temperature by using the idler of the β-BaB₂O₄ parametric oscillator. These interactions preclude the non-phase-matched, cascaded quadratic processes owing to the crystal symmetry along x. The phase-matching properties for these pure cubic processes are presented together with the results on the direct THG of the Nd:YAG laser at 1.0642 μm in three principal planes.

The linear and nonlinear optical properties of Ag_xGa_xGe_1-xS₂ (AGGS) at x = 0.20, 0.25, and 0.50 and Ag_xGa_xGe_1-xSe₂ (AGGSE) at x = 0.17 and 0.25 have been investigated for second-harmonic generation (SHG) of near IR lasers. The polarization dependent transmission curves of these crystals showed larger energy band-gaps for polarization parallel to c axis than that for a axis. The 90° phase-matched SHG wavelengths measured along b axis at room temperature were found to be 0.515, 0.530, and 0.774 μm for the AGGS samples at x = 0.20, 0.25, and 0.50, and 0.638 and 0.676 μm for the AGGSE samples at x = 0.17 and 0.25, respectively. In addition, the crystal to crystal and local variations of the phase-matching conditions are presented together with their temperature stability.

We report on optical parametric oscillator (OPO) based on 2 mm-thick periodically poled Mg-doped stoichiometric LiTaO₃ (PPMgSLT) pumped within the cavity of a Q-switched diode-pumped Nd:YAG laser of high average power that operates at 10 kHz repetition rate. We have obtained 9 W of 2-μm output at the diode current of 21 A from a near-degenerate phase-matched OPO using simple cavity configuration. We also found it has a good long-term stability with such an output of high average power for more than an hour. The intensity profile and measured M² of 2-μm output beam were circularly symmetric and ~7.

A hyperpolarized helium-3 (³He) has been researched extensively for application in fields such as polarization analysis, ³He spin filtration for n (p, d) γ, and medical imaging. In the medical field, nuclear magnetic resonant imaging (MRI) using hyperpolarized gas is attracted recently because air space in human lungs can be monitored in detail by aspirating polarized gas. There are two methods of producing hyperpolarized ³He gas: spin-exchange optical pumping (SEOP) and metastability exchange optical pumping (MEOP). It is well known that the way of making polarization by the MEOP method is more shortly and more directly. In this study, however, the metastable ³He atoms provided by hollow cathode discharge are polarized by circularly polarized light. When ³He atoms pumped optically, the 2³S-2³P transition at the wavelength of 1083nm is leveraged typically. The ³He atom actually has the optical transition 2³S→ 2³P at 389nm, but the transition has never been used. Therefore, we developed the 389-nm coherent light source to polarize ³He gas by MEOP method. This light source utilized the second harmonic generation (SHG) of continuous-wave Ti:sapphire laser operating at a wavelength of 778nm based on BiB₃O₆ (BiBO) in an external cavity.

We present a study of the single pass SHG conversion as a function of the Rayleigh length (RL) and beam diameter (BD) using a monolithic distributed Bragg reflector (DBR) tapered laser. The DBR tapered laser has a 6th order surface grating and a ridge waveguide. Single longitudinal mode emission at 978nm with a side-mode suppression ratio of more than 40dB and at an output power of 2.7W at 15°C have been obtained in continuous wave operation. The beam was collimated using an aspheric and a cylindrical lens and focused using a variety of lenses with various focal lengths. The resulting caustics were acquired using a camera and used for SHG in a 5cm periodically poled LiNbO₃ (PPLN) crystal. This allowed an investigation of the dependency of the SHG conversion efficiency on the RLs and BDs. We obtained 330mW of output power at 488nm using the optimal focus length. The experiments showed that an optimum conversion requires longer focal length's then forecasted by Boyd-Kleinman's theory, which is explained due to the partial coherence. We developed an extension of that theory to account for that partial coherence, which bases in principle on a mismatch related general Agrawal's nonlinear integration kernel. We use this theory to explain the dependence of the SHG efficiency from the beam propagation factor M².

We present our results of nonlinear optical properties of 2(3), 9(10), 16(17), 23(24) tetra tert-butyl phthalocyanine (pc1) and 2(3), 9(10),16(17), 23(24) tetra tert-butyl Zinc phthalocyanine (pc2) studied in solution using Z-scan technique with 800 nm, 100 fsec pulses, 532 nm, 6 nsec pulses and 633 nm continuous wave (cw) laser excitation. Femtosecond open-aperture Z-scan data revealed these molecules exhibited strong 3PA coefficient (α₃). The estimated value of α₃ was ~9.1 × 10^-5 and ~9.5 × 10^-5 cm³/GW² for pc1 and pc2 respectively. Nanosecond open aperture Z-scan studies indicated the presence of strong nonlinear absorption with effective coefficients (α₂) of ~310 and ~420 cm/GW for pc1 and pc2 respectively which are at least two orders higher than the recently reported phthalocyanines. These phthalocyanines also exhibited strong optical limiting properties with nsec excitation with recorded limiting thresholds of ~0.45 J/cm². We observed large nonlinear response in the cw regime at 633 nm. The performance of these alkyl phthalocyanines in various time domains vis-à-vis recently reported phthalocyanines is discussed in detail.

The goal of our research was the construction of the laser emitting short pulses with high peak power in "eye-safe" region around wavelength 1.5 μm. We use Raman self-conversion of giant pulses at wavelength 1.3 μm in Nd³⁺-doped Raman active crystal SrMoO₄ (diameter 4.4 mm, length 42 mm). Fundamental laser wavelength was obtained using this advanced solid-state medium Nd³⁺:SrMoO₄, lasing at 1378.1 nm, and pumped at wavelength 752nm by free-running alexandrite laser. High-peak power required for efficient Raman conversion was reached by Q-switching of the Nd³⁺:SrMoO₄ laser by V:YAG solid-state saturable absorber (initial transmission 93% @ 1380 nm). Specially designed resonator mirrors were used to ensure proper feed-back for Raman laser. The resonator pump mirror was concave with 0.5m curvature and with high transmission at 752nm and high reflectivity in the range from 1250nm to 1580 nm; the reflectivity of the output coupler was 3% @ 1380nm and 25% @ 1570 nm. Both mirrors have reflectivity around 1 μm as small as possible to prevent lasing at other Nd³⁺ lines. With the described laser system, simultaneous generation of wavelengths 1378.1nm and 1569.8nm was obtained. The single pulse output energy 0.8mJ at 1569.8nm was reached. The length of the generated pulse at this wavelength was measured to be 8.7 ns (FWHM). These values correspond with the peak power of 92 kW in eye-safe region.

We report an all-fibre interferometric autocorrelation measurement of femtosecond optical pulses in the C-band. An all-fibre Mach-Zehnder interferometer with piezo-electric fiber stretcher in one arm provides the interference signal. A highly nonlinear and dispersion shifted fibre with Kerr coefficient 10.5 /W-km generates an idler by the process of degenerate four wave mixing of the pump and target pulse signals. The idler intensity is proportional to the interferometric autocorrelation of target pulse. We have measured approximately 100 fs optical pulses at 1552.52nm from an actively mode locked erbium doped fibre laser operating at 280 MHz repetition rate.

We report a singly resonant optical parametric oscillator (SRO) based on a ZnGeP₂ crystal directly-pumped by a lamp-pumped Q-switched CrTmHo:YAG laser. The IR wavelength was tuneable from 4.7 μm to 7.8 μm via crystal angle tuning. A maximum optical to optical efficiency of 56% was obtained from pump (2.09 μm) to total IR at a pump energy of 6.5 mJ. The corresponding idler energy was 1.45 mJ. The SRO was measured to have a slope efficiency of 64% and a threshold of 1 mJ. The spatial beam quality of the idler, characterized by the M² parameter, was 1.38 when the SRO was pumped at 2.5 times threshold. These results show that ZnGeP₂ OPOs directly pumped by a CrTmHo:YAG laser can be operated efficiently, while maintaining good IR beam quality. The wide tuning range and a high pulse energy makes this SRO particularly suitable for spectroscopic applications, and, tests in the field medical application, e.g., for cutting of soft tissue during surgery or corneal corrections.

Ultraviolet single mode laser light is proposed by frequency quadrupling the output of a Nd:YLF laser with two successive frequency doubling stages. For a simple linear cavity laser configuration investigated at 1312 nm, we have optained an intracavity power of 310 W for 16 W of absorbed pump power (λ_p ~ 806 nm). Up to 10 mW tunable single-frequency laser (λ_2W = 656 - 658 nm) is observed. This has been achieved by intracavity second-harmonic generation of a diode-pumped Nd:YLiF₄ linear laser oscillating on the σ-polarized ⁴F_3/2-⁴I_13/2 transition (λ_w ~ 1314 nm) with a β-Barium Borate (BBO) crystal. We also report the experimental measurement of the red-uv conversion efficiency according to the waist size in the BBO crystal. Optained value is compared to those given by the Boyd-Kleinman theory.

Quasi-phase matched (QPM) frequency conversion in ion exchanged potassium titanyl phosphate (KTP) waveguides can be used for highly efficient single pass conversion of low power cw and quasi-cw lasers. Applications include frequency doubling diode lasers for display and biomedical, pulsed sources for fluorescence and remote sensing, and recently KTP waveguides have been used to generate photon pairs using both Type I and II down conversion for quantum information science and technology (QUIST) applications. In this paper, we will describe a nondestructive, all optical technique that can be used to assess the quality and modal index of the ion exchanged waveguide before periodic poling. The structure of the waveguide is interrogated utilizing Type II sum frequency generation (SFG) and is enabled by the fact that the ion exchange process results in waveguides that can support both TE and TM optical modes. The results of this technique can be used to determine the uniformity of the created waveguide and are used to determine the necessary period for a desired poling result. Furthermore, this technique can be utilized to provide an in situ assessment of the poling for any QPM period without needing the laser sources for the particular frequency conversion interaction. Experimental results will be reviewed.

Semi-insulating and conducting SiC crystalline transparent substrates were studied after being processed by femtosecond laser radiation (780nm at 160fs). Z-scan and damage threshold experiments were performed on both SiC bulk materials to determine each samples' nonlinear and threshold parameters. "Damage" in this text refers to an index of refraction modification as observed visually under an optical microscope. In addition, a study was performed to understand the damage threshold as a function of numerical aperture. Presented here for the first time, to the best of our knowledge, is the damage threshold, nonlinear index of refraction, and nonlinear absorption measured values.