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Title: Searching for optimal mitigation geometries for laser resistant multilayer high reflector coatings

Abstract

Growing laser damage sites on multilayer high reflector coatings can limit mirror performance. One of the strategies to improve laser damage resistance is to replace the growing damage sites with pre-designed benign mitigation structures. By mitigating the weakest site on the optic, the large aperture mirror will have a laser resistance comparable to the intrinsic value of the multilayer coating. To determine the optimal mitigation geometry, the finite difference time domain method (FDTD) was used to quantify the electric-field intensification within the multilayer, at the presence of different conical pits. We find that the field intensification induced by the mitigation pit is strongly dependent on the polarization and the angle of incidence (AOI) of the incoming wave. Therefore the optimal mitigation conical pit geometry is application specific. Furthermore, our simulation also illustrates an alternative means to achieve an optimal mitigation structure by matching the cone angle of the structure with the AOI of the incoming wave, except for the p-polarization wave at a range of incident angles between 30{sup o} and 45{sup o}.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1030210
Report Number(s):
LLNL-JRNL-471673
Journal ID: ISSN 0003-6935; APOPAI; TRN: US201124%%14
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Optics
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; APERTURES; COATINGS; CONES; GEOMETRY; INCIDENCE ANGLE; LASERS; MIRRORS; MITIGATION; PERFORMANCE; POLARIZATION; SIMULATION

Citation Formats

Qiu, S R, Wolfe, J E, Monterrosa, A M, Feit, M D, Pistor, T V, and STolz, C J. Searching for optimal mitigation geometries for laser resistant multilayer high reflector coatings. United States: N. p., 2011. Web. doi:10.1364/AO.50.00C373.
Qiu, S R, Wolfe, J E, Monterrosa, A M, Feit, M D, Pistor, T V, & STolz, C J. Searching for optimal mitigation geometries for laser resistant multilayer high reflector coatings. United States. doi:10.1364/AO.50.00C373.
Qiu, S R, Wolfe, J E, Monterrosa, A M, Feit, M D, Pistor, T V, and STolz, C J. 2011. "Searching for optimal mitigation geometries for laser resistant multilayer high reflector coatings". United States. doi:10.1364/AO.50.00C373. https://www.osti.gov/servlets/purl/1030210.
@article{osti_1030210,
title = {Searching for optimal mitigation geometries for laser resistant multilayer high reflector coatings},
author = {Qiu, S R and Wolfe, J E and Monterrosa, A M and Feit, M D and Pistor, T V and STolz, C J},
abstractNote = {Growing laser damage sites on multilayer high reflector coatings can limit mirror performance. One of the strategies to improve laser damage resistance is to replace the growing damage sites with pre-designed benign mitigation structures. By mitigating the weakest site on the optic, the large aperture mirror will have a laser resistance comparable to the intrinsic value of the multilayer coating. To determine the optimal mitigation geometry, the finite difference time domain method (FDTD) was used to quantify the electric-field intensification within the multilayer, at the presence of different conical pits. We find that the field intensification induced by the mitigation pit is strongly dependent on the polarization and the angle of incidence (AOI) of the incoming wave. Therefore the optimal mitigation conical pit geometry is application specific. Furthermore, our simulation also illustrates an alternative means to achieve an optimal mitigation structure by matching the cone angle of the structure with the AOI of the incoming wave, except for the p-polarization wave at a range of incident angles between 30{sup o} and 45{sup o}.},
doi = {10.1364/AO.50.00C373},
journal = {Applied Optics},
number = ,
volume = ,
place = {United States},
year = 2011,
month = 2
}
  • Growing laser damage sites on multilayer high-reflector coatings can limit mirror performance. One of the strategies to improve laser damage resistance is to replace the growing damage sites with predesigned benign mitigation structures. By mitigating the weakest site on the optic, the large-aperture mirror will have a laser resistance comparable to the intrinsic value of the multilayer coating. To determine the optimal mitigation geometry, the finite-difference time-domain method was used to quantify the electric-field intensification within the multilayer, at the presence of different conical pits. We find that the field intensification induced by the mitigation pit is strongly dependent onmore » the polarization and the angle of incidence (AOI) of the incoming wave. Therefore, the optimal mitigation conical pit geometry is application specific. Furthermore, our simulation also illustrates an alternative means to achieve an optimal mitigation structure by matching the cone angle of the structure with the AOI of the incoming wave, except for the p-polarized wave at a range of incident angles between 30 deg. and 45 deg.« less
  • Laser-induced damage in optical coatings is generally associated with micrometer-scale defects. A simple geometric model for nodule-shaped defects is commonly used to describe defects in optical coatings. No systematic study has been done, however, to prove the applicability of that model to an optical coating deposition process. Not all defects have a classic nodule geometry. The present study uses atomic force microscopy (AFM) and scanning electron microscopy to characterize the topography of coating defects in a HfO[sub 2]/SiO[sub 2] multilayer mirror system. Focused ion-beam cross sectioning is then used to study the underlying defect structure. This work develops a modelmore » for defect shape such that the overall geometry of a coating defect, particularly the seed size and depth, can be inferred from nondestructive evaluation measurements such as AFM. The relative mechanical stabilities of nodular defects can be deduced based on the nodule's geometry. Auger analysis showed that the seed material that causes nodular defects in HfO[sub 2]/SiO[sub 2] multilayers is a hafnia oxide. Such characterization capabilities are needed for understanding the enhanced susceptibility of particular defects to laser damage and for developing improved techniques for depositing low-defect density coatings.« less