ANALYSIS OF PICOSECOND MIDINFRARED PULSES BY 2-PHOTON ABSORPTION IN GERMANIUM

We report on the observation of two-photon absorption for the direct g ap in intrinsic germanium at room temperature using two independently tunable picosecond, mid-infrared light pulses. The two-photon absorpti on coefficient is determined for different wavelengths, and carrier de nsities down to about 10(13) cm(-3) could be detected at a sample leng th of 700 mu m. Two-photon absorption in germanium is demonstrated to be a versatile tool for zero-point determination in time resolved pump -probe investigations and permits a precise measure of the time resolu tion of the laser system. (C) 1997 American Institute of Physics.