Energy deposition of pulsed 1.0 micron laser radiation

The absorption of 1.05 micron pulsed laser energy in quiescent argon and hydrogen has been measured. The laser pulse energy varied from 2 to 6J, and the pulse time was 20 ns. The gas pressure varied from 0.3 to 5 atm. A direct optical energy transmission measurement was made by a large time-integrating calorimeter. The trajectory of the blast wave resulting from energy absorption was made visible by use of a Mach-Zehnder interferometer whose light source was a low power, Q-switched Nd-YAG laser. The absorbed energy was inferred from the wave trajectory by means of calculations performed with a one-dimensional (spherically-symmetric) non-steady hydrodynamic code. It was found necessary to use real gas equilibrium thermochemistry in the code to obtain agreement between the absorbed energy measured by optical transmission, and that inferred from the trajectory of the blast wave. Use of perfect gas (constant gamma) code calculations, or ideal blast wave theory, underestimated the absorbed energy. It proved possible to absorb more than 90 percent of the laser pulse energy in both argon and hydrogen at the optimum pressure, which was around 1 atm for argon, and 2 atm for hydrogen.