Intensity and phase evolutions of transmitted and reflected femto-second optical pulses in GaAs

We report on intensity and phase evolutions of transmitted and reflected femto-second optical pulses in bulk (300 μm) and thin film (300 nm) crystals of GaAs by cross-correlation frequency-resolved optical gating method. A beating phenomenon is observed at the transmitted optical pulse through the GaAs thin film. The temporal phase shows a phase jump of almost π, which is equivalent to a change of sign of the field. The oscillatory behavior arises from the interference between upper and lower branches of the polariton excited coherently. The reflection pulse from GaAs thin film shows more complicated behavior in the temporal and spectral domain, because the film is as thick as the wavelength of the optical pulse in the crystal and the polariton effect cannot be ignored. On the other hand, the reflection pulse from bulk GaAs shows an instantaneous pulse response. These phenomena are in good agreement with numerical calculations based on the Lorentz model.