Direct free-hole absorption induced in germanium by 1.06 μm picosecond pulses

The intervalence-band absorption coefficient in germanium is calculated as a function of the hole density and temperature for light with a wavelength of 1.06 μm. At this wavelength, the direct free-hole transitions in germanium occur between the heavy- and split-off hole bands, and between the light- and split-off hole bands. This absorption mechanism is normally negligible compared to the interband absorption; however, for a sufficiently dense electron-hole plasma, the freehole intervalence-band absorption can become comparable to the interband absorption. Furthermore, the interaction of the intense 1.06 μm light alters the distribution of resonantly coupled hole states, and leads to an intensity dependence in the intervalence-band absorption cross section. For a fixed hole density, the intervalence-band cross sections due to free-hole transitions between the heavy- and split-off hole bands and between the light- and split-off hole bands are found to decrease with increasing intensity in a manner closely approximated by an inhomogeneously broadened two-level model. Values for the saturation intensity of each resonant transition are calculated as a function of the hole density and temperature. The intensities required to begin to saturate the direct free-hole transitions are easily attainable using picosecond pulses