Subject of the study. Nonlinear mid-infrared (1.2–2.4 µm) absorption in monocrystalline silicon in the field produced by high-intensity femtosecond laser pulses is studied. Aim of study. Multiphoton absorption coefficients for silicon in the field of high-intensity femtosecond laser pulses in the mid-infrared range are measured to identify efficient modes for laser machining of silicon. Methods. The multiphoton absorption coefficients were estimated by measuring the radiant power transmitted through silicon and then approximating the resulting functions. Main results. The nonlinear optical properties of silicon when excited by high-intensity ultrashort mid-infrared laser pulses were studied. Each absorption event was shown to involve two photons. The two-photon absorption coefficient for wavelengths of 1.2–2.4 µm was shown to be 1.1–0.4 cm/GW. Practical significance. Understanding the process of nonlinear photoionization and obtaining parameters such as the multiphoton absorption coefficients are key factors to take into consideration when selecting efficient modes for laser processing of silicon.
Smirnov et al. (Tue,) studied this question.