Back reflection of short, intense laser pulses at oblique incidence on solid targets is explained with a model where a periodic electron density modulation acts as a diffraction grating. The pump and reflected electromagnetic waves drive through the ponderomotive force the grating and the overall system becomes parametrically unstable. The basic equations governing this system are given. A linearized stability analysis yields the instability growth rate for a homogeneous plasma and the convective gain coefficients for the inhomogeneous case. The results support the feasibility of the suggested mechanism. An absolute instability is predicted to set on at a typical threshold intensity 10¹⁶ W/cm², laser pulse length 100 fs, and spot size 30 micrometers . The instability is shown to saturate at a level of a few percent, because the higher harmonics in the electron density modulation turn the diffraction more diffuse thus reducing both the sustaining ponderomotive force and the back reflection coefficient.

Date Published: 12 March 2001
PDF: 14 pages
Proc. SPIE 4352, Laser Optics 2000: Ultrafast Optics and Superstrong Laser Fields, (12 March 2001); doi: 10.1117/12.418795

Published in SPIE Proceedings Vol. 4352:
Laser Optics 2000: Ultrafast Optics and Superstrong Laser Fields
Alexander A. Andreev; Vladimir E. Yashin, Editor(s)