Laser−supported detonation waves, other laser−supported absorption waves, and plumes of vaporized material were the subject of interferograms. Both instantaneous ruby laser interferometry and time−resolved argon laser interferometry were used to study these events. Qualitative behavior is seen in the interferograms which was not evident in photographic studies of these phenomena, such as the progress of radial shock waves and structure in the absorption zone. Abel inversion is used to obtain quantitative radial behavior of the change in the index of refraction. The differences between the laser−supported absorption waves ignited at the surfaces of several materials are discussed. Alumina specimens produced vapor plumes under these conditions whose temporal motion can be followed because of AlO absorption of the argon laser wavelength. The changes in the index of refraction were measured for similar events at the different wavelengths of the instantaneous and time−resolved interferometers and were used to determine the density profiles of electrons and neutrals. Compared to STP air densities, an ionization of a few percent is seen near a silica surface at laser beam intensities slightly below the ignition threshold for laser−supported detonation waves. An analysis of observed radial shock wave expansion rates predicts a neutral density which, when compared with the density determined from the Abel inversion technique, indicates that the shock front ionization is also a few precent.
In order to investigate approximately the target-zone effects of repetitively pulsed laser beams, two CO, lasers which were focused on the same spot were used in experiments with an adjustable temporal separation between their pUlses. There are reported here studies at 1 atm of the effects of two laser pulses including high-speed photographic and interferometric observations of laser-produced plasmas, shocks, and target vapor; target damage evaluations; and investigations of impulse absorbed by the target. New effects were seen; the most significant of these was the dependence of several of these phenomena on the separation time. The interaction of the second laser pulse with the target is increased when it starts within a window 30 to 70 /Lsec after the start of the first laser pulse.
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