Accession Number:

ADA031852

Title:

Dielectric Breakdown Induced by Picosecond Laser Pulses.

Descriptive Note:

Technical rept. Jan 74-Jun 76,

Corporate Author:

HARVARD UNIV CAMBRIDGE MASS DIV OF ENGINEERING AND APPLIED PHYSICS

Report Date:

1976-10-01

Pagination or Media Count:

180.0

Abstract:

This report contains the consolidated results of investigations, carried out in the period January 1974 - June 1976 on the damage threshold of transparent optical materials. Single picosecond pulses at 1.06 micrometers, 0.53 micrometers and 0.35 micrometers were obtained from a mode-locked Nd-YAG oscillator-amplifier-frequency multiplier system. The pulses are Gaussian in space and time and permit the determination of breakdown thresholds with a reproducibility of fifteen percent. It is shown that the breakdown thresholds reported here are characteristics of the bulk material, which include nine alkali halides, five different laser host materials, KDP, quartz, sapphire and calcium fluoride. The extension of the damage data to the ultraviolet is significant, because some indication is obtained that two- and three-photon absorption processes begin to play a role in determining the threshold. Throughout the visible region of the spectrum the threshold is still an increasing function of frequency, indicating that avalanche ionization is the dominant factor in determining the breakdown threshold. This is confirmed by a detailed study of the damage morphology with a high resolution microscope just above the threshold. A detailed discussion of the influence of self-focusing is given, and evidence for beam distortion below the power threshold for complete self-focusing is presented, confirming the theory of Marburger. Chapter I describes briefly previous work on laser induced breakdown and the relationship of the present work to that described in technical report 643, Laser Induced Damage in Solids, May, 1973, by D. W. Fradin.

Subject Categories:

  • Lasers and Masers
  • Solid State Physics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE