3-PHOTON ABSORPTION IN INAS

Using 125 ps laser pulses, we observe three-photon absorption in room temperature InAs at a wavelength of 9.54 mu m. This effect is readily identified by temperature-tuning the semiconductor bandgap through the three-photon absorption edge. A three-photon absorption coefficient o f K-3 = 1 +/- 0.6 x 10(-3) cm(3) MW-2 is extracted from non-linear abs orption data obtained with an open-aperture Z-scan. Time-resolved meas urement at high irradiance reveals an increase of absorption due to ho t carriers. We also present an autocorrelation measurement of our CO2 laser pulse that shows two complete optical free-induction-decay cycle s.