Semiconductor lasers from photoconductive switch filaments

At the 8th PPC(1991), we reported the first images of current filaments in high-gain photoconductive semiconductor switches(PCSS). Since then many properties of current filaments have been reported, including optical control of their location, shape, and timing. Recently, we have invented a new class of semiconductor laser using these current filaments as the active region in the laser cavity. We have fabricated current filament semiconductor lasers(CFSL) that have produced 75nJ of 890nm radiation in 1.5ns (50W peak), approximately 10 times more energy than conventional (injection-pumped) semiconductor lasers(CSL). These lasers are created from the electron-hole plasma in PCSS current filaments. In contrast to CSL, these new lasers are not based on current-injection. Instead, low-field avalanche carrier generation produces a charge-neutral plasma channel with a carrier distribution for lasing. CFSL are not limited in volume by the depth of p-n junctions (∼1micron). Since we have observed filaments as long as 3.4cm and 400 microns diameter, the active region in CFSL can be more than 100 times larger than in CSL. CFSL larger diameters imply higher energies and reduced divergence in diffraction-limited devices. This presentation reports lasing properties from several configurations of CFSL: high output energies, pulse compression, spectral narrowing, and lasing thresholds. The properties of e-h plasma in PCSS will be compared and contrasted with plasma properties in spark gaps. The CFSL are pulsed and optically triggered like PCSS with the exception that filaments must be created in straight lines using optical line triggers. Potential applications include: active optical sensing/imaging, optical triggers for PCSS, plasma diagnostics, micro-machining, semiconductor scribing, laser ablating, optical communication, and permanent memory.