| Strong spherical shock waves were generated in 1 to 50 torr air by irradiating 3.4-(mu)g 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. The description is consistent with the numerical calculations and not inconsistent with the data. Two-dimensional experiments were conducted by reflecting the spherical shock wave from a plane and by allowing two near-identical shocks to collide. The two-dimensional results are compared to a scaled nuclear shock and to two-dimensional numerical calculations. |
