Extension of the multiple rate equation model for conduction band dynamics under near- and mid-IR femtosecond excitation of dielectrics and semiconductors

Abstract

We present here investigation of theoretical models for conduction band dynamics in solids induced by near- and mid-IR femtosecond laser field. Widely spread Multiple Rate Equation model (MRE) [B. Rethfeld. Phys. Rev. Lett. 92, 187401 (2004)] is considered to be inapplicable when laser wavelength belongs to the near- and mid-IR ranges. We report on an extension of the MRE model and give comprehensive description of the new model. In particular, an additional averaged energy level above the critical one is introduced and phenomenological parameters such as one-photon absorption rate and impact ionization rate are eliminated. The range of laser fluences and wavelengths where the extended model should be used are defined both in narrow and wide bandgap crystals. Bulk micromodification of silicon using 4.5 µm 200-fs laser pulses at laser fluences higher than 0.049 J/cm2 are shown. The proposed Extended Multiple Rate Equation model (EMRE) can be considered as a basis for further theoretical investigation of laser-matter investigation.