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Measurement of the self-focusing threshold in aqueous media by ultrashort laser pulses
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Paper Abstract

Self-focusing is a phenomena that is induced in certain materials when high irradiance laser light interacts with the material. High irradiances are most readily achieved with focused ultrashort laser pulses. Past theoretical calculations using the nonlinear wave equation have calculated the critical power for self-focusing by tightly focused beams in water at 580 nm to be 1 MW. The recent pulse propagation model by Feng et al. has been used to find the pulse duration where the self-focusing threshold can be most easily found. In addition, a first-order model of laser-induced breakdown developed by Kennedy has predicted that the threshold for breakdown at each pulse duration is independent of spot size. Thus self-focusing can be seen from a precise measurement of spot size and breakdown threshold. With several optical setups with different predicted spot sizes, we measured the spot size by knife- edge technique at energies far below the breakdown or self- focusing thresholds for a pulse duration of 2.4 ps, 800 fs, and 126 fs. We also measured the laser-induced breakdown threshold for each of these optical setups. The laser- induced breakdown irradiance threshold was constant for those spot sizes that were below the self-focusing threshold, as predicted by Kennedy's model. The measurements of self-focusing for ultrashort laser pulses in water and its implications on retinal damage will be discussed in this paper.

Paper Details

Date Published: 16 June 1997
PDF: 10 pages
Proc. SPIE 2975, Laser-Tissue Interaction VIII, (16 June 1997); doi: 10.1117/12.275472
Show Author Affiliations
Daniel X. Hammer, Univ. of Texas/Austin (United States)
Gary D. Noojin, TASC (United States)
Robert J. Thomas, TASC (United States)
Richard A. Hopkins, Air Force Armstrong Lab. (United States)
Paul K. Kennedy, Air Force Armstrong Lab. (United States)
Jeffrey J. Druessel, Air Force Armstrong Lab. (United States)
Benjamin A. Rockwell, Air Force Armstrong Lab. (United States)
Ashley J. Welch, Univ. of Texas/Austin (United States)
Clarence P. Cain, TASC (United States)

Published in SPIE Proceedings Vol. 2975:
Laser-Tissue Interaction VIII
Steven L. Jacques, Editor(s)

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