Some characteristics of Co$sub 2$-laser-induced multiple spark breakdown at pressures up to 11 atm

Journal Article · Mon Sep 01 04:00:00 EDT 1975 · J. Appl. Phys., v. 46, no. 9, pp. 3817-3827

OSTI ID:4176103

Morrison, R W; Swail, C

A study has been made of the visible breakdown plasma produced by focusing single TEA CO$sub 2$ laser pulses 200 nsec wide with salt lenses of 16- and 22-cm focal lengths in argon, helium, neon-helium, and nitrogen at pressures up to 11 atm. Pulse energies ranged from 0.9 to 11 J, with a maximum intensity at the 1-mm focal diameter of 6.6times10$sup 9$ W/cm$sup 2$. At this incident intensity, well above the breakdown threshold, the main breakdown plasma in argon occurred well upstream of the focus and its multiple structure extended over 5--9 cm. In the focal region only a few isolated sparks were seen. At incident powers closer to threshold, the breakdown occurred closer to, or at, the focus, and migrated upstream toward the laser as the pressure was increased. The spatial structure of the breakdown plasma as seen by time-integrated photography, and the temporal development, monitored by photon drag observations of the transmitted power pulse, were studied with various gases, pressures, and incident pulse energies. A description of the breakdown process is offered which accounts for many of its features, especially the absence of breakdown in the focal region.

• Research Organization: Physics Department, Carleton University, Ottawa K1S 5B6, Canada
• NSA Number: NSA-33-000277
• OSTI ID: 4176103
• Journal Information: J. Appl. Phys., v. 46, no. 9, pp. 3817-3827, Journal Name: J. Appl. Phys., v. 46, no. 9, pp. 3817-3827; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

*LASER-PRODUCED PLASMA-- THRESHOLD ENERGY
700106* --Fusion Energy--Plasma Research--Plasma Production
ARGON
BREAKDOWN
CARBON DIOXIDE LASERS
ELECTRIC SPARKS
ENERGY TRANSFER
FOCUSING
HELIUM
LASER RADIATION
N70600* --Physics--Controlled Thermonuclear Research-- Production
NEON
NITROGEN
PLASMA DIAGNOSTICS
PRESSURE DEPENDENCE
PULSES