We observe two-photon absorption (2PA) of picosecond, 0.6-μm, 0.3-nJ pulses in a 0.4-μm film of ZnSe. We use high-frequency-modulation phase-sensitive detection to be near the shot-noise limit combined with a low-frequency pulse-delay modulation to discriminate against large thermal nonlinearities. This dual-modulation technique, combined with the field enhancement produced by placing the film in a resonant cavity, permits observation of 2PA and other fast nonlinearities by using pulses having peak powers of the order of 1 W.
© 1988 Optical Society of America
E. W. Van Stryland, Steven A. Miller, M. A. Woodall, and B. S. Wherrett, "Two-photon absorption induced transmission changes in ZnSe interference filters," J. Opt. Soc. Am. B 5, 1289-1292 (1988)