Amorphization of silicon exposed to ultrashort mid-infrared laser pulses

The amorphization of the surface of a 380-$\mu$m-thick crystalline Si(111) wafer exposed to 150-fs ultrashort laser pulses of the mid-infrared region of 4.0–5.4 $\mu$m with variable energy density and exposure time has been experimentally studied. For this spectral range, the threshold fluences for silicon amorphization have been measured. The dependence of the volume fraction and thickness of the amorphous phase of the material on the fluence and the number of laser pulses at a wavelength of 5000 nm has been established.