Accession Number : ADA119786

Title :   Pulsed DF Chain-Laser Breakdown Induced by Maritime Aerosols.

Descriptive Note : Technical rept.,


Personal Author(s) : Amimoto,S T ; Whittier,J S ; Ronkowski,F G ; Valenzuela,P R ; Harper,G N

PDF Url : ADA119786

Report Date : 30 Aug 1982

Pagination or Media Count : 32

Abstract : Thresholds for breakdown induced by liquid and solid aerosols in room air have been measured for a 1 microsec-duration pulsed D2-F2 laser of 3.58 -4.78 micron bandwidth. The DF laser beam was directed into an aerosol chamber that simulated maritime atmospheres on the open sea. Both focus and collimated beams were studied. For a focused beam in which the largest encountered aerosol particles were of 1 to 4 micron diameter, pulsed DF breakdown thresholds were measured to lie in the range 0.6 to 1.8 GW/sq cm. Salt-water aerosol breakdown thresholds for micron-size particles were found to be 15 to 30% higher than the corresponding thresholds for fresh-water particles. For a collimated beam that encountered particle diameters as large as 100 microns, breakdown could not be induced using 0.5- microsec (FWHM) pulses at peak intensities of 59 MW/sq cm. Image converter camera measurements of the radial plasma growth rate of 1.3 cm/microsec (at 1.4 GW/sq cm) were consistent with measurements of the cutoff rate of the transmitted laser beam. Pulsed DF breakdown thresholds of 32 MW/sq cm for 30- micron diameter Al2O3 particles were also measured to permit comparison with the earlier pulsed-HF breakdown results of Lencioni, et al.; the solid-particle threshold measurements agree with the Lencioni data if one assumes that the thresholds for microsecond-duration pulses scales is 1/lambda. An approximate theoretical model of the water particle breakdown process is presented that permits the scaling of the present results to other laser pulse durations, aerosol distributions, and transmission path lengths.

Descriptors :   *Pulsed lasers, *Laser beams, *Measurement, aluminum oxides, Particle size, Aerosols, Light pulses, Solids, Growth(General), Transmittance, Diameters, Dissipation factor

Subject Categories : Lasers and Masers
      Test Facilities, Equipment and Methods

Distribution Statement : APPROVED FOR PUBLIC RELEASE