Laser-Driven Waves in a Freely Expanding Gas Jet

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Abstract
The focused output of a ruby laser has been used to drive waves which travel in the same direction as the laser beam. The density gradient produced by expanding high‐pressure air or hydrogen into a vacuum was irradiated by the laser from the vacuum side of the jet. A luminous plasma was observed to propagate up the jet, through the orifice, and into the gas reservoir. Observations of this type have application to the study of comparable waves generated at the surface of a solid. Measurements of the luminous front velocity are reported over the gas density range of 1–7 amagats and laser power range of 100–500 MW. The scaling relations for this front velocity with laser intensity and gas density are derived for many of the interaction models proposed in the literature. Only the gasdynamic model with fluid motions induced during laser heating compares favorably with the data.