Abstract

Optical erasure rates of optically encoded χ⁽²⁾ gratings in semiconductor microcrystallite-doped glasses (SDG) have been measured for wavelengths above and below the semiconductor bandgap. Exposure of encoded SDG to light above the band gap (ħω>E_g) results in erasure rates ~500 times larger than for ħω>E_g′, indicating that free carriers play an important role. The intensity dependence for ħω>E_g exhibits a surprising dip in the erasure rate with increasing intensity over the range 6-12 W/cm², corresponding to a Debye screening length comparable to the crystallite diameter (d ~ 100 Å). A model for recombination of a trapped carrier with a particle in a 1-D box under a screened electric field predicts the observed intensity dependence if the trapped carrier is assumed to be outside the crystallite. The slow variation of erasure rate with wavelength for ħω>E_g is consistent with ionization of trapped carriers, but the observed erasure rate is 6 orders of magnitude smaller than ionization rates calculated by using matrix elements from a δ-function trap to 3-D box states. If the trap is moved 5-10 Å outside the crystallite, the calculated rates agree with the experimental rates, indicating that the long lived traps used to encode the field are outside the crystallite.

© 1992 Optical Society of America