David Eimerl

Optical, mechanical, and thermal properties of barium borate

We report measurements of all the material constants necessary to fully characterize barium borate as a nonlinear optical material. All data was taken on crystals supplied by Professor Chuangtien Chen, Fuzhou, People’s Republic of China. We have determined the crystal structure, the optical absorption, the refractive indices from the UV to the near IR, the thermo‐optic coefficients, the nonlinear optical or coefficients, the resistance to laser damage, the elastic constants, the thermal expansion, thermal conductivity and dielectric constants, and the fracture toughness. This data is used to evaluate barium borate for a variety of applications. We find that, in general, barium borate has a low acceptance angle, and that despite its higher optical nonlinearity, it is therefore not significantly more efficient than other commonly available materials, except in the UV below 250 nm. On the other hand, it has a high damage threshold, it is physically robust, it has good UV and IR transparency, and it has excel...

Synthesis and characterization of chemical analogs of L-arginine phosphate☆

Abstract L-arginine phosphate is a promising new material for generating harmonics of the Nd: YAG fundamental wavelength, 1064 nm. The synthesis of 20 other salts of L-arginine was attempted and millimeter size crystals of 10 of these were obtained. These were analyzed for crystal structure and chemical composition and the linear and nonlinear optical properties were measured. The compounds were all oprically biaxial and several gave second harmonic signals greater than quartz. Phasematching has been observed in four of the crystals to date.

Deuterated L-arginine phosphate: a new efficient nonlinear crystal

Deuterated L-arginine phosphate (d-LAP) is a highly transparent monoclinic crystal with attractive properties for efficient frequency conversion. It is grown easily from aqueous solution, and it is phase-matchable for all nonlinear processes where KDP is phase-matchable. Over most of its usable frequency range, it is substantially more efficient than KDP. Crystals grown in large sizes (100 cm/sup 3/) have a high damage threshold, excellent optical quality, are less hygroscopic than KDP, and are easily fabricated into nonlinear devices. Deuterated LAP is attractive for harmonic generation of Nd lasers and for work in the ultraviolet down to about 250 nm. >

Raman pulse compression of excimer lasers for application to laser fusion

Application of efficient ultraviolet excimer lasers such as the 248 nm KrF laser to laser fusion requires that long laser pulses be efficiently converted to short pulses at high intensity. The backward Raman amplifier is shown to be a promising candidate for this application. Gain, saturation, and limits to amplifier performance are described. It is shown that pump beams of poor spatial quality may be converted to output beams of high spatial quality. Several common gaseous vibrational Raman scatterers are discussed, and it is shown that a simple KrF-pumped backward Raman amplifier using methane at atmospheric pressure will have a saturation fluence near 1 J/cm2and can produce an output five times as intense as the pump in a ten times shorter pulse with an efficiency of about 50 percent. Design tradeoffs and possible techniques for further improving the performance of such amplifiers are discussed.

High average power harmonic generation

High average power frequency conversion using solid-state nonlinear materials is discussed. Recent laboratory experience and new developments in design concepts show that current technology, a few tens of watts, may be extended by several orders of magnitude. For example, using KD*P, efficient doubling (> 70 percent) of Nd:YAG at average powers approaching 100 KW is possible; for doubling to the blue or UV regions the average power may approach 1 MW. Configurations using segmented apertures permit essentially unlimited scaling of average power. High average power is achieved by configuring the nonlinear material as a set of thin plates with a large ratio of surface area to volume, and cooling the exposed surfaces with a flowing gas. The design and material fabrication of such a harmonic generator is well within current technology.

Research on nonlinear optical materials: an assessment

The seven papers making up this assessment are based on the Workshop on Nonlinear Optical Materials held in April 1986.

Multicrystal designs for efficient third-harmonic generation.

Efficient frequency tripling of high-fluence, narrow-band laser pulses is routinely accomplished with a doubling crystal and a sum-frequency mixer. The addition of a second mixer can dramatically improve conversion efficiencies for the large bandwidths of interest for inertial confinement fusion. Designs that involve two doublers similarly offer a higher dynamic range of conversion efficiency versus intensity than the usual two-crystal design.

Quadrature frequency conversion

A technique for frequency conversion of high-power lasers is described which uses two crystals for each conversion step rather than one. The two crystals are oriented so that the waves generated in them are orthogonally polarized. The conversion efficiency of these quadrature arrangements is much less sensitive to laser pulse nonuniformities than that in single-crystal methods. Consequently, very high conversion efficiency is possible for typically nonuniform laser pulses. Realization of the quadrature concept for all types of nonlinear optical processes are described. Data taken on second harmonic generation of Gaussian pulses shows that very high (internal) conversion efficiency is possible ( > 95 percent) over a substantial range of input energy.

Progress in nonlinear optical materials for high power lasers

Abstract Over the last few years, substantial progress has been made at the Lawrence Livermore National Laboratory in nonlinear materials for high power laser applications. Specifically, we are developing materials for frequency conversion of lasers used in laser driven, thermonuclear fusion experiments and in high average power laser systems. We have developed new experimental procedures for fully characterizing the linear and nonlinear optical properties of microcrystals. Using new theoretical results we have developed a systematic method of selecting and optimizing nonlinear crystals for high-power and high-average-power laser applications. Our molecular engineering strategy for developing new materials for the fusion application has resulted in the discovery of several new materials with more attractive parameters than KDP.

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.