On the wavelength dependence of femtosecond laser interactions inside band gap solids
Résumé
3D laser microfabrication inside narrow band gap solids like semiconductors will require the use of long wavelength intense pulses. We perform an experimental study of the multiphoton-avalanche absorption yields and thresholds with tightly focused femtosecond laser beams at wavelengths: 1.3 mu m and 2.2 mu m. For comparisons, we perform the experiments in two very different materials: silicon (semiconductor, similar to 1.1 eV indirect bandgap) and fused silica (dielectric, similar to 9 eV direct bandgap). For both materials, we find only moderate differences while the number of photons required to cross the band gap changes from 2 to 3 in silicon and from 10 to 16 in fused silica.