Abstract

We have performed picosecond Degenerate Four-Wave Mixing (DFWM) experiments and beam distortion experiments, including using the newly developed Z-scan technique,[1] to accurately measure the bound electronic nonlinear refractive index n₂ in a variety of materials at 1.06 and 0.53 μm. In semiconductors where two-photon absorption (2PA) is allowed, we find that n₂ decreases from its maximum value near the 2PA (2ħω≃E_g) edge to zero as the wavelength is increased, changing to negative nearer the fundamental absorption edge. In order to measure n₂, we experimentally separated the effects of 2PA excited carrier refraction (coefficient σ) from the electronic Kerr effect induced refraction. Using DFWM this is accomplished by observing that the carrier effect lasts for hundreds of picoseconds and varies as the fifth power of the incident irradiance I, while the χ(3) effect follows the temporal variation of the pulse and varies as I³. Such a signal is shown in Fig. 1.

© 1990 Optical Society of America