We report the absorption and scattering losses measurements in IR range by high average power tunable radiation of optical parametric oscillator (OPO) based on a periodically poled lithium niobate (PPLN) pumped by a diode-pumped, Q-switched TEM00 mode Nd:YVO4 laser operated at 1064 nm.

Techniques are presented to model optical nonlinear frequency conversion of highly distorted beams with M-squared values as high as 30. Random superpositions of Gaussian-Hermite modes are used to create the field distributions of the incident beams. Split-step Fourier transform techniques are used for the calculation of nonlinear conversion.

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.

A laser spectrophotometer based on optical parametric oscillators for characterization of optical coatings in the spectral range 420 - 4500 nm is described. The characterization includes measurements of reflectance and transmittance, absorption losses, and laser-induced damage thresholds. The master oscillator of the pump-laser system is a diode-pumped, Q-switched Nd:YAG laser. Additional power, when needed for laser-induced damage threshold measurements, is obtained from flashlamp-pumped Nd:YAG amplifiers. Operation of the laser spectrometer is demonstrated by absorptance measurements and reflectance and transmission measurements of optical coatings over a wide range of angle of incidence. Damage thresholds are measured both with the OPO output and with the direct output and harmonics of the output of the amplified laser system.

Measurements on several high-reflection (HR) metallic mirrors were performed, and multiple-pulse laser induced damage thresholds (LIDT) were estimate according to the draft International Standard ISO/DIS 11254 using S on 1 tests at 1064 nm. The experimental set-up was based on Q-switched, diode-pumped Nd:YAG laser. Transmission increase was used for an in situ measurement of damage. The characteristic damage curves were plotted and multiple-pulse damage thresholds were determined at 30-Hz pulse-repetition rate, while the number of pulses varied up to 300.

We report on the development and use of coherent spectrophotometers specialized for the unusual requirements of characterizing nonlinear optical materials and multilayer dielectric coatings used in laser systems. A large dynamic range is required to measure the linear properties of transmission, reflection and absorption and nonlinear properties of laser-induced damage threshold and nonlinear frequency conversion. Optical parametric oscillators generate coherent radiation that is widely tunable with instantaneous powers that can range from milliwatts to megawatts and are well matched to this application. As particular example a laser spectrophotometer based on optical parametric oscillators and a diode-pumped, Q-switched Nd:YAG laser and suitable for optical characterization in the spectral range 420-4500 nm is described. Measurements include reflectance and transmittance, absorption, scattering and laser-induced damage thresholds. Possibilities of a system based on a 130-fs Ti:sapphire laser and optical parametric generators are also discussed.

The number of laser based biomedical and chemical sensing applications continues to increase. Development and exploitation of many of these applications is limited by the lack of practical laboratory based sources of the required laser radiation. An IR laser/OPO system has been optimized for use in the 5 to 7 μm range. This region includes important water, protein and carbonate absorption bands. Output can be extended to 12 μm if required. The bench top system operates with a multi-wavelength pump laser, which can be configured to operate in the 2.6 to 3 μm region. All three output wavelengths (pump, signal and idler) are available, thus making it suitable for pump-probe experiments. Energy is delivered in single pulses of 50 to 70 ns duration, from 1 to 10 Hz. Depending on the configuration and repetition rate, up to 10 mJ/pulse of signal or idler can be produced.

We report polarization dependent measurements of absorptance of some crystals performed according to the ISO 11551 standard by the "pulse" or "gradient" calorimetric method at 1064 and 532 rim using a pulsed, diode-pumped, Q-switched YAG:Nd laser.

We report the optimization of a periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) pumped by a diode-pumped, Q-switched Nd:YAG laser operated at 1064 nm. Total conversion efficiency exceeding 66 percent was achieved.

We constructed diffusion-bonded stacks of periodically poled lithium niobate (PPLN). Such crystals combine the advantages of planar processing used to make PPLN wafers with the power-handling capability of large apertures. We demonstrated an optical parametric oscillator that uses a 3-mm-thick diffusion-bonded stack consisting of three 1-mm-thick PPLN crystals.

Mid infra-red (IR) sources between 1 μm and 10 μm have wide applications in spectroscopy, remote sensing and military countermeasures. Established nonlinear IR crystals such as AgGaSe2, and AgGaS2 have poor thermal properties, and low damage thresholds. ZnGeP2 appears promising for high power applications, but its growth technology is still being developed, and crystals are expensive. In comparison, GaAs has a large nonlinear coefficient, good optical transmission between 1 μm and 12 μm, and high optical damage threshold. It also has good chemical stability, good mechanical properties, and a well developed growth technology. Unfortunately, single crystal GaAs is linearly isotropic; therefore, nonlinear interactions cannot be birefringently phase-matched. However, the interacting waves can be quasi-phasematched (QPM) by periodically modulating the nonlinear coefficient in a stack of rotated plates1,2. By diffusion bonding individual plates together, we can minimize scattering and reflection losses at the air-GaAs interfaces. Preliminary diffusion-bonded-stacked (DBS) GaAs devices demonstrated close to theoretical conversion efficiency3,4, but had high transmission losses. We report improved processing, leading to a significant reduction in the transmission loss to less than 0.2% per layer at 5 μm.

We review progress of quasi-phasematched (QPM) optical parametric oscillators (OPOs) in bulk periodically poled LiNbO3. Using the electric field poling process, we can reliably fabricate 0.5-mm thick crystals with uniform domain structures over 15-mm long. Periodically poled material retains the low loss and bulk power handling properties of single domain LiNbO3, and QPM allows noncritical phasematching with the highest value of the nonlinear coefficient. OPOs pumped by 1.064-micrometers pulsed Nd:YAG lasers have been operated over the wavelength range 1.45 micrometers to 4.0 micrometers with tuning by temperature or QPM period. We have shown oscillation threshold as low as 0.020 mJ with a Q-switched pump laser, and pumping over two times threshold without damage. We have also demonstrated a doubly resonant oscillator near 1.96 micrometers pumped directly with a cw diode laser at 978 nm.

We report a widely tunable quasi-phase-matched optical parametric oscillator that uses periodically poled LiNbO(3)with a multigrating structure. The device is tuned by translation of the crystal through the resonator and pump beam, with no realignment needed. With a 1.064-microm acousto-optically Q-switched Nd:YAG pumplaser, we produced noncritically phase-matched tunable IR output from 1.36 to 4.83 microm. The threshold was 6 microJ for a 26-mm interaction length. The extraordinary polarization of LiNbO(3) has better IR transmission than does the ordinary polarization, permitting operation at longer wavelengths with d(33) quasi-phase matching than with conventional Type I birefringent phase matching.

We report a quasi-phase-matched optical parametric oscillator, using bulk periodically poled LiNbO3. The optical parametric oscillator, pumped by a 1.064-mum Q-switched Nd:YAG laser, was temperature tuned over the wavelength range 1.66-2.95 mum. The oscillation threshold of almost-equal-to 0.1 mJ was more than a factor of 10 below the damage limit. The LiNbO3 crystal, fabricated by application of an electric field to a sample with liquid and metal surface electrodes, was 0.5 mm thick with a 5.2-mm interaction length and a quasi-phase-matched period of 31 mum.

We report a quasi-phase-matched optical parametric oscillator, using bulk periodically poled LiNbO(3). The optical parametric oscillator, pumped by a 1.064-microm Q-switched Nd:YAG laser, was temperature tuned over the wavelength range 1.66-2.95 microm. The oscillation threshold of approximately 0.1 mJ was more than a factor of 10 below the damage limit. The LiNbO(3) crystal, fabricated by application of an electric field to a sample with liquid and metal surface electrodes, was 0.5 mm thick with a 5.2-mm interaction length and a quasi-phase-matched period of 31 microm.

were filtered by two pieces of 3-pm-thick beryllium foils (the absorption edge; at 111.5 eV), and exposed a Si specimen. After traveling 50 cm through a flight tube, photoelectrons were detected by a twostage microchannel plate, and photoelectron current signals were recorded with a digitizing oscilloscope. In the talk, the expected performance of our system will be discussed in detail by showing obtained photoelectron spectra of various materials. *Electrotechnical Laboratory, 1-1-4 umezono, Tsukuba, lbaraki 305, Japan. 1. H. Ade, J. Kirz, S. L. Hulbert, E. D. Johnson, E. Anderson, D. Kem, "Xray spectromicroscopy with a zone plate generated microplobe", Appl. Phys. Lett. 56, 1841-1843 (1990).