PASSAGE OF LASER-LIGHT THROUGH A HOLE-PLASMA SHUTTER

The interaction of a plasma produced by irradiation of perforated foil s with laser pulses was studied. The laser beam of the first harmonics of the iodine laser (lambda = 1.315 mu m) system PERUN was focused by an f/2 optics (f = 20 cm) on a hole in the foil target of high-Z mate rial. The laser energy and the temporal shape of the pulses were monit ored both before and behind the hole. Foils of two different materials (Pb, Cu) were used, and a series of hole diameters 2r(H) ranging from 100 mu m to 500 mu m were tested. The diameter of the laser focal spo t 2r(0) was about 150 mu m. For hole diameters smaller than 300 mu m, a shortening of the laser pulse was observed, demonstrating the effect of plasma shutter. The pulse shortening, which depends on the hole di ameter, corresponds to the reduction in the pulse energy passing throu gh the hole. An analysis of the experimental data is based on hydrodyn amic computations, and the physics of the process is illustrated by a simple analytical model.