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Early Heating Processes in Laser-Supported Detonation (LSD) Wave Initiation on Metals and Alloys.

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Final rept. 15 Aug 76-15 Aug 78,

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This report presents results of a two-year experimental study of early heating processes on metal and alloy surfaces under pulsed laser irradiation conditions which are known to give rise to so-called laser-supported detonation LSD waves at 10.6 micrometers. The results are applicable to the understanding of LSD-wave initiation as well as to the understanding of pulsed heating of metals in general. The approach consisted of studying the time-resolved specular reflectivity of metal samples subjected to intense TEA CO2 laser radiation 50-100 ns pulse width in a vacuum. The experimental configuration was selected to give a high degree of beam homogeneity on the sample surface. Metallographic examination of samples was performed to correlate changes in the surface structure with reflectivity results. Metals studied included aluminum, copper, iron, nickel, titanium, Al 2024, and Ti-6-4. The data obtained were the first of their kind recorded at 10.6 micrometers and revealed an anomalous effect in the specular reflectivity transient. The effect consisted of a sharp drop in reflectivity midway in the pulse to a low value 5-40 followed by recovery to nearly the initial value late in the pulse. The effect was studied most extensively with aluminum, but was found to occur generally in the other materials irradiated. Considerable differences in thresholds and details of the effect were found which were attributable to materials effects and alloying.

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  • Lasers and Masers
  • Metallurgy and Metallography

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