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Title: Evaluation of UV absorption coefficient in laser-modified fused silica

Abstract

Laser-induced damage in transparent dielectrics leads to the formation of laser-modified material as a result of exposure to extreme localized temperatures and pressures. In this work, an infrared thermal imaging system in combination with a fluorescence microscope is used to map the dynamics of the local surface temperature and fluorescence intensity under cw, UV excitation of laser-modified fused silica within a damage site. The energy deposited via linear absorption mechanisms and the absorption coefficient of the modified material are estimated based on a thermal diffusion model. In addition, irreversible changes in the absorption following extended laser exposure were observed.

Authors:
; ; ; ; ;  [1]
  1. Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550-0808 (United States)
Publication Date:
OSTI Identifier:
20971805
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 90; Journal Issue: 6; Other Information: DOI: 10.1063/1.2472775; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ABSORPTION; EXCITATION; FERROELECTRIC MATERIALS; FLUORESCENCE; LASERS; MICROSCOPES; SILICA; THERMAL DIFFUSION; ULTRAVIOLET SPECTRA

Citation Formats

Negres, R. A., Burke, M. W., Sutton, S. B., DeMange, P., Feit, M. D., and Demos, S. G.. Evaluation of UV absorption coefficient in laser-modified fused silica. United States: N. p., 2007. Web. doi:10.1063/1.2472775.
Negres, R. A., Burke, M. W., Sutton, S. B., DeMange, P., Feit, M. D., & Demos, S. G.. Evaluation of UV absorption coefficient in laser-modified fused silica. United States. doi:10.1063/1.2472775.
Negres, R. A., Burke, M. W., Sutton, S. B., DeMange, P., Feit, M. D., and Demos, S. G.. Mon . "Evaluation of UV absorption coefficient in laser-modified fused silica". United States. doi:10.1063/1.2472775.
@article{osti_20971805,
title = {Evaluation of UV absorption coefficient in laser-modified fused silica},
author = {Negres, R. A. and Burke, M. W. and Sutton, S. B. and DeMange, P. and Feit, M. D. and Demos, S. G.},
abstractNote = {Laser-induced damage in transparent dielectrics leads to the formation of laser-modified material as a result of exposure to extreme localized temperatures and pressures. In this work, an infrared thermal imaging system in combination with a fluorescence microscope is used to map the dynamics of the local surface temperature and fluorescence intensity under cw, UV excitation of laser-modified fused silica within a damage site. The energy deposited via linear absorption mechanisms and the absorption coefficient of the modified material are estimated based on a thermal diffusion model. In addition, irreversible changes in the absorption following extended laser exposure were observed.},
doi = {10.1063/1.2472775},
journal = {Applied Physics Letters},
number = 6,
volume = 90,
place = {United States},
year = {Mon Feb 05 00:00:00 EST 2007},
month = {Mon Feb 05 00:00:00 EST 2007}
}
  • Laser-induced damage in transparent dielectrics leads to the formation of laser-modified material as a result of exposure to extreme localized temperatures and pressures. In this work, we used an infrared thermal imaging system in combination with a fluorescence microscope to map the dynamics of the local surface temperature and fluorescence intensity under cw, UV excitation of laser-modified fused silica within a damage site. Based on a thermal diffusion model, we estimate the energy deposited via linear absorption mechanisms and derive the absorption coefficient of the modified material. In addition, irreversible changes in the absorption following extended laser exposure were observed.
  • The presence of strong nonlinear absorption has been observed in laser modified fused silica. Intensity-dependent transmission measurements using 355-nm, 532-nm and 1,064-nm laser pulses were performed in pristine polished regions in fused silica substrates and in locations that were exposed to dielectric breakdown. The experimental results suggest that multi-photon absorption is considerably stronger in the modified regions compared to pristine sites and is strongly dependent on the excitation wavelength.
  • Numerical simulations on UV-laser-induced densification of fused silica have been performed using classical molecular dynamics. The effect of laser irradiation is modeled by the energy transfer from the absorbed laser photons to the bonded silicon and oxygen atoms, i.e., the thermal effects of laser-irradiation on silica glass. Results from simulations at various laser pulse duration, pressure, and temperature conditions show that longer laser pulse duration, higher pressure, and higher temperature cause larger densification. We have also compared the microstructural and elastic properties of fused silica desndified by UV-laser and hydrostatic pressure, respectively. Similar change sare observed in both cases; severalmore » notable differences are noticed, too, and include Si-O bond length change, number of over-coordinated atoms, and ring distributions.« less
  • Point defects are induced in high quality optical-grade fused silica by high fluence (>30 J/cm{sup 2}) 355nm laser pulses. The microscopic depth distribution of laser irradiation induced defects has been nondestructively determined using Cathodoluminescence (CL) microanalysis. CL emissions have been observed at 1.9eV, 2.2eV, 2.7eV and 4.4eV. In addition following CO{sup 2} laser treatment for damage mitigation an emission at 3.2eV is also observed. The CL emissions have been identified with the NBOHC (non-bridging oxygen hole center), the STE (self-trapped exciton), an ODC (oxygen-deficient center) and an aluminum impurity centre. The spatially resolved CL data is consistent with damage initiationmore » at the exit surface. The concentration of 355 nm laser induced defects is greatest at the surface and monotonically decays to pre-irradiation levels at {approx}10 {micro}m depth below the surface. With CO{sup 2} processing to mitigate damage, the defect concentration and spatial distribution is reduced to a maximum depth of {approx}6{micro}m. CL microanalysis provides a sensitive and nondestructive method of assessing the magnitude and submicron distribution of irradiation induced damage in technologically important materials.« less
  • Waveguides were written in fused silica using both a femtosecond fiber laser with a 1 MHz pulse repetition rate and a femtosecond amplified Ti:sapphire laser with a 1 kHz repetition rate. Confocal Raman and fluorescence microscopy were used to study structural changes in the waveguides written with both systems. A broad fluorescence band, centered at 650 nm, associated with non-bridging oxygen hole center (NBOHC) defects was observed after waveguide fabrication with the MHz laser. With the kHz laser system these defects were only observed for pulse energies above 1 {mu}J. Far fewer NBOHC defects were formed with the MHz lasermore » than with kHz writing, possibly due to thermal annealing driven by heat accumulation effects at 1 MHz. When the kHz laser was used with pulse energies below 1 {mu}J, the predominant fluorescence was centered at 550 nm, a band assigned to the presence of silicon clusters (E{prime}{sub {delta}}). We also observed an increase in the intensity of the 605 cm{sup -1} Raman peak relative to the total Raman intensity, corresponding to an increase in the concentration of 3-membered rings in the lines fabricated with both laser systems.« less