Abstract

We report the first low-temperature nonlinear optical studies of Bi_1−xSb_x thin films grown by molecular-beam epitaxy (MBE). Third-order nonlinear susceptibilities χ⁽³⁾ were determined from nondegenerate-four-wave-mixing experiments by using a pair of grating-tuned, synchronously Q-switched CO₂ lasers, which generate ≈150-ns pulses. Because Bi_1−xSb_x has a large index of refraction (>10) and that of the BaF₂ substrate is low, both the front surface and the interface with the substrate have high reflectivities, and significant Fabry-Perot enhancement of the nonlinear response occurs. For the ≈0.5-µm-thick samples discussed here, the round-trip optical path length of ≈10 µm is nearly equal to the CO₂ laser wavelength.

© 1991 Optical Society of America