Measurements of 50 fs nonlinear gain time constant in semiconductorlasers

The symmetric and asymmetric nonlinear gain in 1.3-μm semiconductor lasers were measured in the frequency domain by a novel pump-probe technique using an external cavity traveling-wave semiconductor ring laser. A very short time constant of about 50 fs was measured as the dominant process. The data also indicated the presence of a smaller contribution approximately 15% of the magnitude of the dominant process and with a long time constant consistent with the effect of hot carriers