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Title: Scalable process for mitigation of laser-damaged potassium dihydrogen phosphate crystal optic surfaces with removal of damaged antireflective coating

Abstract

Here, we investigate an approach for the recycling of laser-damaged large-aperture deuterated potassium dihydrogen phosphate (DKDP) crystals used for optical switching (KDP) and for frequency conversion (DKDP) in megajoule-class high-power laser systems. The approach consists of micromachining the surface laser damage sites (mitigation), combined with multiple soaks and ultrasonication steps in a coating solvent to remove, synergistically, both the highly adherent machining debris and the laser-damage-affected antireflection coating. We then identify features of the laser-damage-affected coating, such as the “solvent-persistent” coating and the “burned-in” coating, that are difficult to remove by conventional approaches without damaging the surface. We also provide a solution to the erosion problem identified in this work when colloidal coatings are processed during ultrasonication. Finally, we provide a proof of principle of the approach by testing the full process that includes laser damage mitigation of DKDP test parts, coat stripping, reapplication of a new antireflective coat, and a laser damage test demonstrating performance up to at least 12 J/cm 2 at UV wavelengths, which is well above current requirements. Our approach ultimately provides a potential path to a scalable recycling loop for the management of optics in large, high-power laser systems that can reduce cost and extendmore » lifetime of highly valuable and difficult to grow large DKDP crystals.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Physical and Life Sciences and NIF and Photon Sciences
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1366904
Alternate Identifier(s):
OSTI ID: 1345553
Report Number(s):
LLNL-JRNL-712417
Journal ID: ISSN 0003-6935; APOPAI
Grant/Contract Number:
AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Applied Optics
Additional Journal Information:
Journal Volume: 56; Journal Issue: 8; Journal ID: ISSN 0003-6935
Publisher:
Optical Society of America (OSA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 42 ENGINEERING

Citation Formats

Elhadj, S., Steele, W. A., VanBlarcom, D. S., Hawley, R. A., Schaffers, K. I., and Geraghty, P. Scalable process for mitigation of laser-damaged potassium dihydrogen phosphate crystal optic surfaces with removal of damaged antireflective coating. United States: N. p., 2017. Web. doi:10.1364/AO.56.002217.
Elhadj, S., Steele, W. A., VanBlarcom, D. S., Hawley, R. A., Schaffers, K. I., & Geraghty, P. Scalable process for mitigation of laser-damaged potassium dihydrogen phosphate crystal optic surfaces with removal of damaged antireflective coating. United States. doi:10.1364/AO.56.002217.
Elhadj, S., Steele, W. A., VanBlarcom, D. S., Hawley, R. A., Schaffers, K. I., and Geraghty, P. Tue . "Scalable process for mitigation of laser-damaged potassium dihydrogen phosphate crystal optic surfaces with removal of damaged antireflective coating". United States. doi:10.1364/AO.56.002217. https://www.osti.gov/servlets/purl/1366904.
@article{osti_1366904,
title = {Scalable process for mitigation of laser-damaged potassium dihydrogen phosphate crystal optic surfaces with removal of damaged antireflective coating},
author = {Elhadj, S. and Steele, W. A. and VanBlarcom, D. S. and Hawley, R. A. and Schaffers, K. I. and Geraghty, P.},
abstractNote = {Here, we investigate an approach for the recycling of laser-damaged large-aperture deuterated potassium dihydrogen phosphate (DKDP) crystals used for optical switching (KDP) and for frequency conversion (DKDP) in megajoule-class high-power laser systems. The approach consists of micromachining the surface laser damage sites (mitigation), combined with multiple soaks and ultrasonication steps in a coating solvent to remove, synergistically, both the highly adherent machining debris and the laser-damage-affected antireflection coating. We then identify features of the laser-damage-affected coating, such as the “solvent-persistent” coating and the “burned-in” coating, that are difficult to remove by conventional approaches without damaging the surface. We also provide a solution to the erosion problem identified in this work when colloidal coatings are processed during ultrasonication. Finally, we provide a proof of principle of the approach by testing the full process that includes laser damage mitigation of DKDP test parts, coat stripping, reapplication of a new antireflective coat, and a laser damage test demonstrating performance up to at least 12 J/cm2 at UV wavelengths, which is well above current requirements. Our approach ultimately provides a potential path to a scalable recycling loop for the management of optics in large, high-power laser systems that can reduce cost and extend lifetime of highly valuable and difficult to grow large DKDP crystals.},
doi = {10.1364/AO.56.002217},
journal = {Applied Optics},
number = 8,
volume = 56,
place = {United States},
year = {Tue Mar 07 00:00:00 EST 2017},
month = {Tue Mar 07 00:00:00 EST 2017}
}

Journal Article:
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  • Measurements of the magnitude and the sign of certain quadratic electro-optic coefficients of potassium dihydrogen phosphate (KDP) and ammonium dihydrogen phosphate (ADP) were made with an actively stabilized Michelson interferometer. The results obtained for these coefficients are, in units of 10{sup -20}m{sup 2}V{sup -2} (as opposed to literature values of order 10{sup -18}m{sup 2}V{sup -2}), as follows: (KDP)g{sub xxxx}=-3.4{+-}0.5, g{sub yyxx}=-0.2{+-}0.4, and g{sub zzxx}=-0.7{+-}0.4; (ADP)g{sub xxxx}=-7.4{+-}1.0, g{sub yyxx}=-1.7{+-}0.9, and g{sub zzxx}=-1.4{+-}0.9. The quadratic Faust--Henry coefficient describing the lattice and the electronic contributions to the quadratic electro-optic effect in KDP and ADP is estimated from our results. These show that themore » nonlinear susceptibility responsible for the quadratic electro-optic effect in these crystals is due mainly to nonlinear interactions of the low-frequency electric field with the crystal lattice. {copyright} 2001 Optical Society of America« less
  • Potassium dihydrogen phosphate KH{sub 2}PO{sub 4} (KDP) is a transparent dielectric material best known for its nonlinear optical and electro-optical properties. Because of its nonlinear optical properties, it has been incorporated into various laser systems for harmonic generation and optoelectrical switching. In addition, KDP is particularly suitable for use in large-aperture laser systems such as that located at the National Ignition Facility (NIF) because it can be grown as a single crystal to large size. Despite the importance of this material, surface composition and surface electronic structure data were found to be nonexistent. X-ray photoemission spectroscopy was thus used tomore » characterize the composition and surface structure of (100) and (101) native crystals.« less
  • Potassium dihydrogen phosphate (KDP) is widely used for high-power laser frequency conversion. Its applications, however, are limited by a characteristically low laser damage threshold. This damage is associated with extrinsic impurity inclusions, whose exact nature has not been previously identified. We have now demonstrated that KDP grown in solutions containing organic impurities incorporates select organic compounds into the crystal matrix. Furthermore, we have observed a strong correlation between the concentration of these compounds and the crystal laser damage threshold and density.
  • A model for the description of laser-induced damage in bulk potassium dihydrogen phosphate (KDP) by nanosecond laser pulses is addressed. It is based on the heating of nanometric plasma balls whose absorption efficiency is described through the Mie theory. The plasma optical indices are then evaluated within the Drude model framework. This modeling provides an evaluation of the scaling law exponent x linking the damage threshold laser pulse energy density F{sub c} to the pulse duration {tau} as F{sub c}={alpha}{tau}{sup x}, where {alpha} is a constant. The inverse problem for which the knowledge of experimental data allows one to determinemore » physical parameters of the model is considered. The results suggest that the critical plasma density is reached in a time much shorter than the pulse duration. Information about the nature of defects responsible for the damage initiation is also provided.« less