Mark S. Webb

Second-harmonic generation in zinc tris(thiourea) sulfate

The linear and second-order nonlinear optical properties of single-crystal zinc tris(thiourea) sulfate, or ZTS, are determined. The deduced nonlinear coefficients are |d(31)| = 0.31, |d(32)| = 0.35, and |d(33)| = 0.23 pm/V compared with a |d(14)| value of 0.39 pm/V for potassium dihydrogen phosphate. Because it exhibits a low angular sensitivity (deltaDeltak/deltatheta), ZTS may prove useful for type-II second-harmonic generation from 1.06 to 1.027 microm. We present the phase-matching measurement data for ZTS and compare the calculated frequency conversion efficiency for ZTS with that of several other well-characterized materials.

Phase-matched harmonic generation in lithium triborate (LBO)

The authors present refractive index, thermo-optic, phase-matching angle, nonlinear coefficient, absorption, and scattering data on lithium triborate (LBO) crystals. They briefly discuss the material quality of the crystals, including the results of calorimetric absorption measurements in the infrared and ultraviolet. They present a new set of refractive index values with better than fourth decimal place precision, as well as measurements of the thermo-optic parameters. The nonlinear coefficients and other frequency conversion parameters of LBO were investigated by studying the phase-matched generation of Nd:YAG harmonics. These results are summarized. The authors discuss angular and thermal bandwidths for phase matching. Finally, they compare the efficiency of LBO with that of several other frequency conversion crystals for a common commercial application-the generation of Nd:YAG harmonics. >

High-average-power KTiOAsO4 optical parametric oscillator.

Using noncritically phase-matched 1-cm(2) -aperture KTiOAsO(4) (KTA) crystals in an optical parametric oscillator (OPO), we have demonstrated a sustained average signal power of 33 W at 1534.7 nm. To our knowledge, this is the highest-average-power signal ever generated by an OPO. The pump source was a 100-Hz Q -switched 1064-nm Nd:YAG laser. Compared with that of the similar and more-common material KTiOPO>(4) , idler absorption in KTA is negligible, allowing high-power operation with minimal thermally induced refractive distortion in the OPO crystal.

Wavelength insensitive phase-matched second-harmonic generation in partially deuterated KDP

We have experimentally determined the spectrally noncritical phase-matching behavior of type I frequency doubling in potassium dihydrogen phosphate (KDP) and its dependence on deuteration level in partially deuterated KD*P. Our results are in agreement with predictions based on available refractive-index data. The first-order wavelength-sensitivity parameter ∂Δk/∂λ for type I doubling of 1.053-μm light vanishes for a KD*P crystal with a deuteration level of 12 ± 2%. Calculations of this effect in other KDP analogs are presented, and the possibility of finding materials that have spectrally noncritical behavior for other phase-matched processes is discussed.

Nonlinear optical properties of K/sub 2/La(NO/sub 3/)/sub 5/.2H/sub 2/O and K/sub 2/Ce(NO/sub 3/)/sub 5/.2H/sub 2/O

The harmonic generating properties of potassium lanthanum nitrate (KLN) and potassium cerium nitrate (KCN) are described. These crystals have much larger nonlinear coefficients than potassium dihydrogen phosphate (KDP) and are nearly noncritically phase matched at room temperature for Type I frequency doubling of 1.064- mu m light, and for Type II doubling of light near 0.95 mu m. Thus, these crystals are useful for generating blue-green light by frequency doubling high-power near-infrared lasers. The crystal growth of KLN and KCN are described by the three component phase diagrams. Crystallographic data for KCN that confirms its structural similarity to KLN are presented. The optical absorption spectra of the two materials are discussed, and the linear refractive indexes are given. >

Temperature sensitivity of phase-matched second-harmonic generation in LiIO/sub 3/

Measurements were made of the temperature dependence (between 23 and 65 degrees C) of the phase-matching angle theta /sub pm/ for type I frequency doubling of 1064-nm laser light in lithium iodate (LiIO/sub 3/). The measured value of d theta /sub pm//dT is -14.7+or-1 mu rad/ degrees C, which corresponds to a thermal sensitivity beta /sub T/=0.24+or-0.02 cm/sup -1// degrees C for this process. Also calculated is a value of d theta /sub pm//dT using experimentally determined thermooptic data available in the literature. The calculated value of d theta /sub pm//dT is -31+or-18 mu rad/ degrees C using literature values of n and dn/dT for LiIO/sub 3/. The extreme sensitivity of the calculated value of d theta /sub pm//dT to small errors in the thermooptic coefficients may be the reason for this discrepancy. >

Temperature sensitivity of KDP for phase-matched frequency conversion of 1 /spl mu/m laser light

The magnitudes of the derivatives of the phase-matching angles with respect to temperature |/spl part//spl theta//sub pm///spl part/T| (milli-radians/degree celsius), for critically phase-matched frequency conversion using KDP (KH/sub 2/PO/sub 4/) have been directly measured for the five most interesting processes to inertial confinement fusion (ICF) laser-system designers: 2/spl omega/ I, 2/spl omega/ II, 3/spl omega/ I, 3/spl omega/ II, and 4/spl omega/ I. These measurements span an approximate temperature range of 25 to 90/spl deg/C, and were performed at a fundamental (1/spl omega/) wavelength of /spl lambda/=1.064 pm. The results are used to calculate the phase-matching thermal-sensitivity parameter |/spl beta//sub T/| (centimeter/sup -1//milliradian), for each conversion process. >

Multi-wavelength injection seeded mid-infrared optical parametric oscillator for DIAL

We have constructed and fielded a multi-wavelength injection seeded mid-IR OPO source for DIAL. This OPO system was built for ground based remote sensing measurements of species with both broad (300 cm-1) and narrow absorption bandwidth (0.07 cm-1 FWHM). The OPO utilizes a single frequency tunable diode laser for the injection seeded signal wavelength in the region from 6400 to 6700 cm-1 and an angle phase-matched 5 cm LiNbO3 crystal to provide large tuning excursions on a slow time scale. The pump was a diode pumped Nd:YAG MOPA (9398 cm-1) running at 180 Hz. This pump source was repeatedly injection seeded with a different wavelength on each of three sequential shots forming a set of three pulses having wavelength separations on the order of 0.4 cm-1 at a three color set repetition rate of 60 Hz. This combination of OPO signal and pump source produced a set of three time staggered idler wavelengths separated by 0.4 cm-1 with the center wavelength tunable from 2700 to 3000 cm-1. This OPO system was used in field test experiments to detect the release of chemicals from a standoff distance of 3.3 Km. We present key OPO design criteria, performance data, and numerical simulations that agree with our observation of pump induced spectral impurities in the OPO output.

Second and third order nonlinear optical properties of crystalline inorganic/organic complexes

Properties for members of a new class of nonlinear optical (NLO) materials which stoichiometrically incorporate organic and inorganic constituents into a single crystalline lattice are reported. Recent results for our synthetic, crystal growth, and optical studies suggest that a number of these relatively transparent ``semiorganic`` compounds have significant second and/or third order NLO responses and often display favorable crystal growth morphologies. The prototype material of this class zinc tris(thiourea) sulfate, or ZTS, has a UV cutoff at about 325 nm, can be readily grown to cm{sup 3} sizes, and has been shown to be a highly efficient Type II frequency doubler for 1064 nm Nd:Yag laser radiation. ZTS also processes a moderate third order nonlinear optical response (ca. 0.1{times}CS{sub 2}) which occurs on at least a picosecond time scale as determined by degenerate four-wave mixing (DFWM) experiments at 532 nm. Refractive index, second harmonic generation, and DFWM data for a number of these new compounds are presented.

High-bandwidth second-harmonic generation in partially deuterated KDP

We have experimentally determined the spectrally noncritical phasematching behavior of Type I frequency doubling in KDP and its dependence on deuteration level in partially deuterated KDP. The first order wavelength sensitivity parameter (alpha) (Delta) k/(alpha) (lambda) for Type I doubling of 1.053 micrometers light vanishes for a KD*P crystal with a deuteration level between 10 and 14%. Very high bandwidth frequency doubling of Nd:glass lasers is possible with such a crystal.