Performance of semiconductor current filament lasers

We present performance and modeling results for a new class of semiconductor laser that can potentially produce much more short pulse energy than conventional (injection-pumped) semiconductor lasers. High energy operation is possible because this new laser is not limited in volume or aspect ratio by the depth of a p-n junction. These lasers are created from current filaments in semi-insulating GaAs where low-field avalanche carrier generation produces a high-density, charge-neutral plasma channel having the required carrier density distribution for lasing. We have tested current filament semiconductor lasers (CFSL) that have produced 75 nJ of 890 nm light in 1.5 ns (50 W peak), approximately ten times more energy than conventional lasers. Current filaments as long as 3.4 cm and several hundred microns in diameter have been observed in our high-gain GaAs photoconductive switches. The smallest dimension of these filaments can be more than 100 times the carrier diffusion length in GaAs. It is this large active volume that enables the observed high laser output energy. This paper reports spectral narrowing, lasing thresholds, beam divergence, temporal narrowing, and energies for several configurations of CFSL. We also discuss results from models developed to simulate the unusual gain phenomena and mechanism for obtaining transparency within the electron-hole plasma of the current filament