skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: A Summary of Recent Damage-Initiation Experiments on KDP Crystals

Abstract

We summarize recent investigations of the density and morphology of bulk damage in KDP crystals as a function of pulse duration, temporal profile, wavelength, and energy fluence. As previously reported by Runkel et al., we also find that the size of bulk damage sites varies roughly linearly with pulse duration for pulses between 1 ns and 9 ns. However this trend no longer applies at pulse durations below 1 ns. Experiments measuring the damage density and size distribution as a function of wavelength confirm many previous works which indicated a strong dependence of damage density with wavelength. However, we also find that the size of damage sites is relatively insensitive to wavelength. Further we see damage due to Flat-In-Time (FIT) pulses has different pulse length and fluence dependence than Gaussian pulses. We demonstrate that a simple thermal diffusion model can account for observed differences in damage densities due to square and Gaussian temporally shaped pulses of equal fluence. Moreover, we show that the key laser parameter governing size of the bulk damage sites is the length of time the pulse remains above a specific intensity. The different dependences of damage density and damage site size on laser parameters suggest differentmore » absorption mechanisms early and late in the damaging pulse.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
887280
Report Number(s):
UCRL-PROC-216929
TRN: US200618%%44
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Presented at: Boulder Damage Symposium XXXVII, Boulder, CO, United States, Sep 19 - Sep 22, 2005
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; ABSORPTION; DISTRIBUTION; LASERS; MORPHOLOGY; THERMAL DIFFUSION; WAVELENGTHS

Citation Formats

Carr, C W, Feit, M D, Rubenchik, A M, Trenholme, J B, and Spaeth, M L. A Summary of Recent Damage-Initiation Experiments on KDP Crystals. United States: N. p., 2005. Web.
Carr, C W, Feit, M D, Rubenchik, A M, Trenholme, J B, & Spaeth, M L. A Summary of Recent Damage-Initiation Experiments on KDP Crystals. United States.
Carr, C W, Feit, M D, Rubenchik, A M, Trenholme, J B, and Spaeth, M L. Mon . "A Summary of Recent Damage-Initiation Experiments on KDP Crystals". United States. doi:. https://www.osti.gov/servlets/purl/887280.
@article{osti_887280,
title = {A Summary of Recent Damage-Initiation Experiments on KDP Crystals},
author = {Carr, C W and Feit, M D and Rubenchik, A M and Trenholme, J B and Spaeth, M L},
abstractNote = {We summarize recent investigations of the density and morphology of bulk damage in KDP crystals as a function of pulse duration, temporal profile, wavelength, and energy fluence. As previously reported by Runkel et al., we also find that the size of bulk damage sites varies roughly linearly with pulse duration for pulses between 1 ns and 9 ns. However this trend no longer applies at pulse durations below 1 ns. Experiments measuring the damage density and size distribution as a function of wavelength confirm many previous works which indicated a strong dependence of damage density with wavelength. However, we also find that the size of damage sites is relatively insensitive to wavelength. Further we see damage due to Flat-In-Time (FIT) pulses has different pulse length and fluence dependence than Gaussian pulses. We demonstrate that a simple thermal diffusion model can account for observed differences in damage densities due to square and Gaussian temporally shaped pulses of equal fluence. Moreover, we show that the key laser parameter governing size of the bulk damage sites is the length of time the pulse remains above a specific intensity. The different dependences of damage density and damage site size on laser parameters suggest different absorption mechanisms early and late in the damaging pulse.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Nov 07 00:00:00 EST 2005},
month = {Mon Nov 07 00:00:00 EST 2005}
}

Conference:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

Save / Share:
  • Considerable attention has been paid over the years to the problem of growing high purity KDP and KD*P to meet damage threshold requirements of ICF lasers at LLNL. The maximum fluence requirement for KD*P triplers on the National Ignition Facility (NIF) is 14.3 J/cm 2 at 351 nm in a 3 ns pulse. Currently KD*P (conventional or rapid grown) cannot meet this requirement without laser (pre)conditioning. In this overview, recent experiments to understand laser conditioning and damage phenomena in KDP and KD*P will be discussed. These experiments have lead to a fundamental revision of damage test methods and test resultmore » interpretation. In particular, the concept of a damage threshold has given way to measuring performance by damage distributions using millimeter sixed beams. Automated R/l (conditioned) damage tests have shown that the best rapidly grown KDP crystals exhibit the same damage distributions at the best conventionally grown KD*P. Continuous filtration of the growth solution and post growth thermal sealing are shown to increase the damage performance as well. In addition, centimeter size beams from multijoule lasers have been used to study stepwise laser conditioning in KDP. These tests have shown that an increase in the damage threshold of ~1.5X is attainable with 8-12 shots of increasing fluence. The experiments show that the damage density (pinpoints/mm 3) evolves exponentially and once formed, the micron sized bulk pinpoints remain stable against increases in local fluence. The information obtained from damage distributions and conditioning studies has been used with model NIF spatial profiles to determine the probability of damage and the local pinpoint density generated in a tripler. Calculations based on test data have shown that .for well conditioned, high quality rapid growth KDP or conventional growth KD*P the damage probability is less than 3%. Furthermore, the fluence profiles expected on NIF lead to only small numbers of generated pinpoints which are not expected to adversely affect NIF operations. To check the validity of the results, the 37 cm KD*P tripler from the Beamlet laser was mapped for damage. The inspection revealed pinpoint densities of the order of predicted by the damage evolution calculations« less
  • We present the results of laser damage measurements conducted on potassium dihydrogen phosphate (KDP) and deuterated potassium dihydrogen phosphate (KD*P) crystals that were grown recently for both production and research applications by several sources. We have measured extrinsic damage thresholds that cover wavelengths from 1064 nm to 266 nm at pulse durations in the 3- to 10-ns regime. Many of the samples were extracted from boules grown specifically to yield large-area crystals, up to 32-cm square, for laser fusion applications. These crystals were the result of efforts, both by the Lawrence Livermore National Laboratory (LLNL) and commercial crystal-growth companies, tomore » yield high-threshold KDP. In particular we have established that such crystals can reliably survive fluences exceeding 15 j/cm[sub 2] at 355 nm and 20 j/cm[sup 2] at 1064 nm when irradiated with 3-ns pulses. We present details of how bulk and surface damage to these crystals scale with pulse duration and wavelength as well as of morphological effects due to laser conditioning.« less
  • Investigated is the influence of isotermal annealing on the real structure and laser damage threshold of KDP single crystals. It is shown that the annealing of the samples at temperatures close to that of phase transition results in a pronounced decrease of the number of defects in the crystals, their optical homogeneity being improved. The chosen optical annealing conditions allow to raise the values of mechanical strength and laser damage threshold by 2 or 3 times and thereby to reduce the spread of these characteristics over the bulk of the crystals.
  • The paper is devoted to studing the influence of Ca, Si, Pb and Cr impurities (possessing no absorption bands at the wavelength of acting laser irradiation) on the value of bulk laser damage threshold and UV absorption in KDP single crystals. It is shown that for the investigated 5 concentration range (1 {divided_by}10{sup -5} mass%) laser damage treshold essentially decreases with raising the concentration of impurity ions in the crystal lattice. The maximal value of the said characteristic ({approximately}40 J/cm{sup 2}) is found to be achieved in the case when the concentration of impurities is not less than 1 {divided_by}{supmore » -5} mass %.« less
  • We report the experimental results of impurity contamination and laser-induced damage investigations on rapidly grown potassium dihydrogen phosphate (KDP) crystals. Using absorption spectroscopy and chemical analysis, we determined the impurity distribution in the different growing sectors of KDP single crystals. The level of impurity was dependent on the starting materials and growth rate. We also studied the influence of impurities on the laser-induced damage in fast grown KDP. The laser damage threshold in the impurity-rich prismatic sector is same as in the high purity pyramidal sector within the experimental error. Meanwhile, the laser damage threshold (LDT) at the boundary ofmore » the prismatic and pyramidal sectors is less than half of that in the bulk. Furthermore, we found that the thermal annealing of the crystal eliminated the weakness of this sector boundary and increased its LDT to the same level as in the bulk of the crystal. Our result suggests that laser damage occured in the vicinity of a high, localized strain field.« less