Measurements of absorption coefficient and refractive index changes without the Kramers-Kronig relation in photorefractive quantum wells of GaAs

We measure the absorption coefficient and refractive index changes produced in photorefractive quantum wells of GaAs by using a high-sensitivity periodically phase-modulated two-wave mixing technique. The technique allows us to measure both the amplitude and phase of the refractive and absorption index changes simultaneously. Thus, there is no necessity to use the Kramers-Kronig relation when either the absorption or refractive index is known. We also measure the response time of the grating 2 formation in the frequency domain, yielding similar to15 mus at I-0 = 11 mW cm(-2), which shows that quantum wells of GaAs are one of the fastest materials for dynamic holography.