Modeling KDP Bulk Damage Curves for Prediction of Large-Area Damage Performance
Over the past two years extensive experimentation has been carded out to determine the nature of bulk damage in KDP. Automated damage testing with small beams has made it possible to rapidly investigate damage statistics and its connection to growth parameter Variation. Over this time we have built up an encyclopedia of many damage curves but only relatively few samples have been tested with large beams. The scarcity of data makes it difficult to estimate how future crystals will perform on the NIF, and the campaign nature of large beam testing is not suitable for efficient testing of many samples with rapid turn-around, it is therefore desirable to have analytical tools in place that could make reliable predictions of large-beam performance based on small-beam damage probability measurements. To that end, we discuss the application of exponential and power law damage evolution within the framework of Poisson statistics in this memo. We describe the results of fitting these models to various damage probability curves on KDP including the heavily investigated KDP214 samples. We find that both models are capable of fitting the damage probability S-curves quite well but there are multiple parameter sets for each model that produce comparable {chi}{sup 2} values. In addition, the fit parameters from the exponential model do not agree well with the measured evolution from large-beam OSL experiments where pinpoint density was shown to evolve according to n(F)=n{sub 0}exp(bF). The largest discrepancy is in determination of the b values. For the O'Connell formalism the power law case developed here, we find that the best-fit powers have approximately the same magnitude as the Weibull exponent of Feit's formalism, but it is difficult to extract information about the defect concentration using the O'Connell approach. In addition, we found that the power law case provides slightly better {chi}{sup 2} values in roughly half of the cases. We discuss these results in terms of fluence measurement precision and the observed fluctuation of damage density observed on OSL testing. We conclude that these two formalisms are not yet well-enough developed to provide reliable parameters for predicting large-scale damage performance of KDP. In outlining possible steps for refining the models, we also call for any future small-spot damage model to include the effects of laser conditioning.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE Office of Defense Programs (DP) (US)
- DOE Contract Number:
- W-7405-Eng-48
- OSTI ID:
- 791057
- Report Number(s):
- UCRL-JC-134766; TRN: US0301501
- Resource Relation:
- Conference: 31st Boulder Damage Symposium: Annual Symposium on Optical Materials for High Power Lasers, Boulder, CO (US), 10/04/1999--10/07/1999; Other Information: PBD: 16 Dec 1999
- Country of Publication:
- United States
- Language:
- English
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