Abstract

As much as 25% self-diffraction has been observed at the surface of n-GaAs:Te when two pumps (and a weak probe) intersect with an internal angle of 0.15 rad in the Raman–Nath regime. The photoinduced gratings decayed in less than 100 ps. The diffraction efficiency was nearly independent of sample thickness (40 μm and 350 μm), and careful investigation has shown that the diffraction arose primarily at the surface and was resonant just below the band edge. It is proposed that band-bending at the surface states causes increased absorption and results in a sheet of optically induced charge. The faster diffusion of electrons relative to holes allows a transient charge separation to a distance of one diffusion length (1 μm). As a result, a space-charge field is formed (Dember field) that can cause an index change through the Franz–Keldysh effect. The resulting transient grating can cause the large observed diffraction. This new BEST effect has potential for optical-switching applications.

© 1990 Optical Society of America