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Monte Carlo simulation of the R/1 automated damage test

Description: In this paper, a Monte Carlo computer analysis of the R/l automated damage test procedure currently in use at LLNL is presented. This study was undertaken to quantify the intrinsic sampling errors of the R/l ADT method for various types of optical materials, particularly KDP and fused silica, and to provide a recommended minimum number of test sites. A gaussian/normal distribution of 10 J/cm² average fluence ({mu}) was used as a damage distribution model. The standard deviation ({sigma}) of the distribution was varied to control its shape. Distributions were simulated which correspond to the damage distributions of KDP ({mu}/{sigma} = 5-10) and fused silica ({mu}/{sigma} - 15). A measure of the variability in test results was obtained by random sampling of these distributions and construction of the cumulative failure probability �S� curves. The random samplings were performed in runs of 100 �tests� with the number of samples (i.e. sites) per test ranging from 2 to 500. For distributions with {mu}/{sigma} = 5-10, the study found an intrinsic error of 3 to 5% in the maximum deviation from the distribution average when using 100 site tests. The computations also showed substantial variation in the form of the CFD for any given test. The simulation results were compared to actual data from eight 100 site R/l automated tests on a sample from rapidly grown KDP. It was found that while each 100 site damage probability curve could be fit to a gaussian distribution reasonably well, the 800 site cumulative damage probability curve was better modeled by a lognormal distribution. The differences observed in the individual CFD curves could be accounted for by sampling errors calculated from gaussian models.
Date: September 18, 1998
Creator: Runkel, M
Partner: UNT Libraries Government Documents Department

Measuring parameters of large-aperture crystals used for generating optical harmonics

Description: The purpose of this project was to develop tools for understanding the influence of crystal quality and crystal mounting on harmonic-generation efficiency at high irradiance. Measuring the homogeneity of crystals interferometrically, making detailed physics calculations of conversion efficiency, performing finite- element modeling of mounted crystals, and designing a new optical metrology tool were key elements in obtaining that understanding. For this work, we used the following frequency-tripling scheme: type I second- harmonic generation followed by type II sum-frequency mixing of the residual fundamental and the second harmonic light. The doubler was potassium dihydrogen phosphate (KDP), and the tripler was deuterated KDP (KD*P). With this scheme, near-infrared light (1053 nm) can be frequency tripled (to 351 nm) at high efficiency (theoretically >90%) for high irradiance (>3 GW/cm&sup2;). Spatial variations in the birefringence of the large crystals studied here (37 to 41 cm square by about 1 cm thick) imply that the ideal phase-matching orientation of the crystal with respect to the incident laser beam varies across the crystal. We have shown that phase-measuring interferometry can be used to measure these spatial variations. We observed transmitted wavefront differences between orthogonally polarized interferograms of {lambda}/50 to {lambda}/100, which correspond to index variations of order 10<sup>-6</sup>. On some plates that we measured, the standard deviation of angular errors is 22-23 &micro;rad; this corresponds to a 1% reduction in efficiency. Because these conversion crystals are relatively thin, their surfaces are not flat (deviate by k2.5 urn from flat). A crystal is mounted against a precision-machined surface that supports the crystal on four edges. This mounting surface is not flat either (deviates by +2.5 &micro;m from flat). A retaining flange presses a compliant element against the crystal. The load thus applied near the edges of the crystal surface holds it in place. We performed detailed finite-element ...
Date: February 23, 1999
Creator: Auerbach, J M; English, R E, Jr; Hibbard, R L; Michie, R B; Norton, M A; Perfect, S A et al.
Partner: UNT Libraries Government Documents Department

Impurity leaching rates of 1000 liter growth tanks

Description: This memo reports on the analysis of some recent measurements of solution impurity levels in the three KDP and one DKDP Pilot Production 1000 liter growth tanks (Tanks B, C, D, & F). Solution samples were taken on a weekly basis during recent crystal growth runs in each tank and were analyzed by inductively coupled plasma emission spectroscopy (ICP-ES). The solution history for five specific elements, Si, B, Al, Fe and Ca will be analyzed in detail. The first four of these elements are input into solution via slow dissolution of the glass vessel at a rate which is strongly dependent on the solution temperature. Si and B continuously accumulate in solution, since they are not incorporated into the crystal. Al and Fe by comparison are incorporated into the crystal (primarily the prismatic sectors) and present problems to inclusion-free growth (Al) and 30 damage (Fe). The level of these impurities initially increases when the crystal size is small but later decreases when the rate of incorporation into the crystal exceeds the rate of dissolution of the glass tank. The last element, Ca is of interest since it has recently been observed to be one of the elements found at the location of 3cu damage. For Si and B, the dissolution or leach rate from the glass tank is easily obtained from the results of the chemical analysis. The temperature dependent leach rates are shown to be comparable (within a factor of two) for all four tanks, with Tank B (DKDP) having the lowest rate of Si accumulation. The glass leach rates of the two incorporating elements Al and Fe require substantially more analysis as the daily variation of the crystal dimensions, the solution concentration, and the mass of KDP remaining in solution must be taken into account in order to ...
Date: February 19, 1999
Creator: Burnham, A; Floyd, R; Robey, H F & Torres, R
Partner: UNT Libraries Government Documents Department

Modeling of frequency doubling and tripling with converter refractive index spatial non-uniformities due to gravitational sag

Description: Accurate predictions of the performance of frequency conversion requires knowledge of the spatial variation of departures from the phase-matching condition in the converter crystals. This variation is caused by processes such as crystal growth and crystal surface finishing. Gravitational sag and mounting configurations also lead to deformation and stresses which cause spatially varying departures from the phase-matching condition. We have modeled the effect of gravitational forces on conversion efficiency performance of horizontal converter crystals and have shown for the NIF mounting configurations that gravity has very little effect on conversion efficiency. Keywords: Frequency conversion, ICF, Nonlinear optics, KDP crystals
Date: August 3, 1998
Creator: De Yoreo, J J; Auerbach, J M; Barker, C E; Couture, S A; Eimerl, D; Hackel, L A et al.
Partner: UNT Libraries Government Documents Department