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Title: A multi-dimensional investigation of laser conditioning in KDP and DKDP crystals

Abstract

We present a multi-parametric experimental investigation of laser conditioning efficiency and behavior in KDP and DKDP crystals as a function of laser wavelength, fluence, number of pulses, and conditioning protocol. Our results expose complex behaviors associated with damage initiation and conditioning at different wavelengths that provide a major step towards revealing the underlying physics. In addition, we reveal the key parameters for optimal improvement to the damage performance from laser conditioning.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
886671
Report Number(s):
UCRL-CONF-216863
TRN: US200616%%1096
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Presented at: Boulder Damage Symposium, Boulder, CO, United States, Sep 19 - Sep 21, 2005
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 42 ENGINEERING; EFFICIENCY; LASERS; PERFORMANCE; PHYSICS; WAVELENGTHS

Citation Formats

DeMange, P, Negres, R A, Carr, C W, Radousky, H B, and Demos, S G. A multi-dimensional investigation of laser conditioning in KDP and DKDP crystals. United States: N. p., 2005. Web.
DeMange, P, Negres, R A, Carr, C W, Radousky, H B, & Demos, S G. A multi-dimensional investigation of laser conditioning in KDP and DKDP crystals. United States.
DeMange, P, Negres, R A, Carr, C W, Radousky, H B, and Demos, S G. Mon . "A multi-dimensional investigation of laser conditioning in KDP and DKDP crystals". United States. doi:. https://www.osti.gov/servlets/purl/886671.
@article{osti_886671,
title = {A multi-dimensional investigation of laser conditioning in KDP and DKDP crystals},
author = {DeMange, P and Negres, R A and Carr, C W and Radousky, H B and Demos, S G},
abstractNote = {We present a multi-parametric experimental investigation of laser conditioning efficiency and behavior in KDP and DKDP crystals as a function of laser wavelength, fluence, number of pulses, and conditioning protocol. Our results expose complex behaviors associated with damage initiation and conditioning at different wavelengths that provide a major step towards revealing the underlying physics. In addition, we reveal the key parameters for optimal improvement to the damage performance from laser conditioning.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Oct 31 00:00:00 EST 2005},
month = {Mon Oct 31 00:00:00 EST 2005}
}

Conference:
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  • The laser-induced damage performance of KDP and DKDP nonlinear crystals following pre-exposure to lower-energy laser pulses (laser annealing, also known as laser conditioning) is investigated as a function of wavelength for both, the damaging and conditioning pulses. To obtain a quantitative evaluation of damage performance of the material, we measure the density of damage events as a function of laser parameters. This new method allows for a detailed assessment of the improvement of material performance from laser conditioning and reveals the key parameters for optimizing performance depending on the operational wavelength.
  • The interaction of damage initiating defect precursors in KDP and DKDP crystals with laser pulses is investigated as a function of laser parameters to obtain experimental results that contain information about the type and nature of the defects. Specifically, the focus is to understand (a) the interaction of the precursors with sub-damage laser pulses leading to improvement to the damage performance (laser conditioning) and (b) the synergetic effects during multi-wavelength irradiation. Our results expose complex behaviors of the defect precursors associated with damage initiation and conditioning at different wavelengths that provide a major step towards revealing the underlying physics.
  • Currently, most of our thinking about the defects responsible for initiating laser damage considers them as featureless absorbers. However, an increasing body of evidence, particularly involving multi-wavelength irradiation, suggests electronic structure of damage initiators is important in determining both initiation and conditioning behaviors in KDP. The effective absorption coefficient of energy under multi-wavelength irradiation cannot be accounted for by a structureless absorber, but is consistent with an initiator with a multi-level structure. We outline the evidence and assess the ability of such a simple multi-level model to explain these and other experimentally observed behaviors.
  • Large solid state lasers such as Beamlet and the proposed National Ignition Facility (NIF) require optical materials with extremely high damage thresholds. Potassium dihydrogen phosphate (KDP) and its deuterated analog (KD*P) both require some form of conditioning to reach the design fluence of these lasers. Both the bulk material and the crystal surfaces must have damage thresholds in excess of 16J/cm{sup 2} at 1053 nm and 11J/cm{sup 2} at 351 nm for 3-ns pulselengths. The use of ultrafiltration techniques has been demonstrated to produce bulk material with damage thresholds exceeding these requirements with the use of R:1 laser conditioning. Moremore » recent results at LLNL using large-area laser conditioning and thermal annealing are described for a variety of state-of-the-art KDP and KD*P crystals. Results on thermally annealed KD*P with a deuteration range of 60% to 80% are also presented, and compared to those of ordinary KDP.« less
  • Laser conditioning by raster scanning KDP and DKDP crystals using Nd:YAG and XeCl excimer laser systems was demonstrated. The laser systems were evaluated to determine their respective feasibility of improving the damage thresholds of the harmonic materials for use on the National Ignition Facility (NIF). Crystals were first evaluated using an Nd:YAG laser (355 nm, 7.6 ns) by scanning 2 x 2 cm2 areas with sub-damage threshold fluences and then performing unconditioned (SA) damage tests at 355-nm in the respectively scanned regions. Subsequently, five KDP and DKDP samples of various damage quality were raster scanned in a similar fashion atmore » MicroLas GmbH (Goettingen, Germany) using a commercial Lambda Physik Excimer system (XeCl, {lambda} = 308 nm, 20 ns). The samples treated in Germany were then tested at Livermore National Laboratory (LLNL) at 355 nm to demonstrate the excimer's potentia1 as an alternative conditioning source. The excimer scan results suggest that crystals can be treated at high fluence (50 Ycm2, 308-nm, 204s) levels without noticeable bulk damage. In addition, comparable conditioning is possible even with the fluence set at 30% of the 308-nm damage threshold. The laser damage tests with 355-nrn on the majority of the excimer laser-treated crystals demonstrates the effect of conditioning, by raising the SI1 threshold or by reducing the low fluence tail of the 355-nm S/1 damage probability curves. Furthermore, the high average power and flat top beam profile of an excimer laser makes it possible to laser condition a 42-crn NIF-size crystal in one day, compared to 41 days for a commercial table-top Nd:YAG system. The test samples were to be particularly susceptible to surface damage during excimer raster conditioning, possibly due to high levels of dust and/or contaminants in the laboratory environment.« less