Abstract

Studies of the high speed modulation response of semiconductor lasers, exhibited a strong damping of the relaxation oscillation resonance and suggested the presence of a nonlinear gain process with a characteristic time much shorter than the carrier lifetime^[1]. Several possible mechanisms were proposed which might produce this nonlinear gain, including spectral hole burning, carrier heating, and four wave mixing related effects^[2]. CW studies have been performed in an effort to indentify these nonlinear gain mechanisms^[2,3]. However, time domain femtosecond measurements have the advantage that they can directly characterize the ultrafast gain dynamics. Several single-wavelength femtosecond pump-probe investigations were performed on various diode laser systems^[4,5]. Carrier heating effects and spectral hole burning were reported, but to date, no direct femtosecond measurements of the wavelength dependence of spectral hole buring have been possible.

© 1994 Optical Society of America