Abstract

ZnSe has been shown to exhibit strong nonlinear absorption for bulk and epitaxially grown samples¹ due to bandfilling and coulomb screening. Consequently, one can expect very strong self-action effects, which, in turn, may be used to determine the nonlinear refractive index Δn(I, λ) (Ref. ²) as function of both the laser intensity I and the wavelength λ, using either self- focusing² or self-bending.³ In this experiment we used a 10-ns pulsed dye laser beam with λ ~ 450 nm and intensities up to ~10 MW cm⁻² to achieve these self-action effects. Bulk and epitaxially grown (on GaAs) films⁴ with thicknesses of ~500 and ~1 μm, respectively, were used, and the samples were cooled to 77 K. The laser beam was focused onto the sample. The spatial intensity distribution in the far field area displayed strong self-focusing and self-bending, which were measured and used to determine Δn(I, λ). These two methods for obtaining the nonlinear refractive index give qualitatively consistent results. In bulk ZnSe at λ ≈ 450 nm we observe the onset of self-action effects at I ≈ 300 kW / cm². In the nonlinear case, a sharp band edge with a width of ~1.8 nm (corresponding to roughly kT) was measured, which we attribute to the saturation of the band-edge tail, i.e., bandfilling effects. In addition to self-focusing and self-bending, the large nonlinear refractive index of this material enabled us to demonstrate other nonlinear propagation effects.

© 1989 Optical Society of America