Picosecond optically-induced intervalence band absorption in germanium

By using a mode-locked Nd: glass laser with much improved beam properties, we have observed the onset of direct intervalence band absorption at 1.06 μm in germanium at excitation levels between 225 MW/cm 2 (≈2 mJ/cm 2 ) and 10 GW/cm 2 (≈75 mJ/cm 2 ). This absorption limits the transmission to a maximum value well below that expected for complete saturation of the direct valence-to-conduction band absorption coefficient by band filling.