Femtosecond Transport and Space-Charge Field Formation in Semiconductors Using the Photorefractive Effect.

During the project we put together and developed a titaniumsapphire mode-locked laser. The output of the laser was characterized as optical pulses between 100 to 200 femtoseconds in duration. The laser was tunable between 900 nanometers and 1000 nanometers. This tuning range is ideal for studies on indium phosphide. The laser could also be operated in the continuous wave mode. In addition to building and characterizing the laser we used the laser to carry out an investigation of the photorefractive behavior of indium phosphide. In particular, we characterized the two wave mixing gain. We found the gain to display an intensity dependent resonance. That is, as predicted by theory, we found the gain to peak at a given intensity. Also, as predicted by theory, we found the relative phase between the intensity spatial pattern and the space-charge field spatial pattern to depend on the intensity. In particular, our measurements demonstrated, for the first time, that the relative phase was 0 degrees for low intensities, that it was 90 degrees at intensity for which the gain peaked and that it was near 180 degrees for high intensities. As a result of our work it is clear that the photorefractive model for indium phosphide is accurate and that it can be used to determine the sign of the photocarrier, drift length, diffusion length, mobility, and dopant concentration. jg p1