Abstract

We recently obtained the dispersion and band-gap scaling of the bound electronic Kerr effect (n₂) from a nonlinear Kramers-Kronig transformation of the nondegenerate nonlinear absorption spectrum calculated including the AC Stark, electronic Raman, and two-photon absorption effect.¹ The results for the degenerate case gave excellent agreement with the experimental results of semiconductors as well as large gap dielectrics.² We have extended this formalism to obtain a general expression for the nondegenerate n₂(ω₁; ω₂) and 2PA coefficient β(ω₁; ω₂). This allows us to calculated the change of refractive index (Δn) and absorption (Δα) at a probing frequency ω₁, due to the presence of a pump beam at ω₂ < ω_g. Experiments were performed using a excite-probe (two-color) Z-scan technique.²,³ Picosecond pulses from a mode-locked Nd:YAG laser at λ₂ = 1.06 μm were used as the pump beam while the second harmonic of these pulses at λ₁ = 0.532 μm probed the induced nonlinearities in two-color Z-scan geometry. Here the pump beam induces a Kerr lens in the sample, which changes the transmittance of the probe beam as transmitted through an aperture in the far field. This change is a strong function Z position (along the propagation distance) of the sample.

© 1991 Optical Society of America