We measure the efficiency of converting high-power 15-fs 0.8-mum pulses to the mid infrared in GaAs and GaSe as well as the pulse duration and the spectrum of the infrared radiation that is produced. Free-carrier production limits the conversion efficiency in GaAs to approximately 5 x 10(-7), allowing us to produce 2.5-pJ, 30-fs pulses spanning the spectral range from 6 to 14 mum. In GaSe we obtain, in a moderately saturated regime, a conversion efficiency of 7.5 x 10(-5), limited by two-photon absorption, allowing us to produce pulses of 100-fs duration containing 10 nJ of energy. (C) 2001 Optical Society of America.