Abstract

Laser-matter interaction with intense (10¹⁶- 10¹⁸ W/cm²) picosecond pulses has been investigated experimentally for two essentially different cases of laser front steepness (Fig. 1). The two rising pulse fronts cause a prepulse or a prepulse-free interaction. Absorption of laser radiation as well as spectral modifications in the backscattered fundamental wave and its second harmonic were measured for various angles of incidence and some values of laser flux density. It is supposed that the red and blue frequency shifts of the backscattered waves observed are associated with Doppler shifts corresponding to inward or outward movement of the critical density surface in dependence on the shape of the laser pulse front.

© 1994 Optical Society of America