Light-induced gaps in semiconductor band-to-band transitions

A triplet around the third harmonic of the semiconductor band gap was observed when exciting 50-100 nm thin films GaAs films with 5 fs pulses at 3 × 10²² W/cm². It was shown that this triplet in the optical spectrum was a result of light-induced gaps in the band structure, which arise from coherent band mixing. The 5 fs linearly polarized optical pulses from a Ti:sapphire mode-locked laser oscillator were employed which focused onto the GaAs film, held at room temperature, by means of a high numerical aperture reflective microscope objective. The GaAs layers of thickness l were grown directly on sapphire substrate in a molecular-beam epitaxy machine.