Laser shock-wave generation, propagation and interactions in low-pressure air

Strong spherical shock waves were generated in 1 to 50 torr air by irradiating 3.4 micrograms plastic shell targets with 5 to 30 J, 300 psec Nd:glass laser pulses. The shock wave trajectories were measured with an electrostatic framing camera during the luminous phase and a shadowgraphy system during the nonluminous phase. A holographic, two wavelength interferometer obtained both trajectory information and fringe patterns which, after Abel inversion, yielded electron and gas density profiles. The data taken during the early expansion when the target mass has a significant effect were compared with existing analytical calculations and with numerical calculations. A description of the early expansion is given, in which the target mass is taken to be an isentropically expanding gas that supplies energy to a variable energy blast wave in the surrounding air.