Two-color ultrafast spectroscopy of semiconductor quantum wells

Femtosecond spectroscopy such as two color pump-probe and four-wave mixing (FWM) on GaAs quantum wells has been performed using two partially synchronized, independently tunable lasers with external jitter compensation. In the two beam and three beam ((omega) 1, (omega) 1; (omega) 2) four wave mixing experiments, heavy-and-light-hold beatings are observed with these two mutually incoherent lasers. FWM signals are observed when (omega) 2 is completely below the exciton energies, with no spectral overlap with the absorption profile. These off-resonant signals are stronger than the interband continuum signals for equivalent detunings. Femtosecond frequency mixing (2(omega) 1- (omega) 2) is also demonstrated when the grating is formed by two different frequencies.