Abstract

The third-order nonlinear optical susceptibility χ⁽³⁾ accounts for a great variety of physical processes in nonlinear optics.¹ For the generation and propagation of ultrashort optical pulses the intensity-dependent refractive index n =n₀ + n₂Iis of particular importance, where n₂(ω) ~ χ⁽³⁾(ω,–ω,ω). If the frequency dependence of n₂(ω) is negligible in a broad frequency region, i.e. the main contributions to χ⁽³⁾ (ω,–ω,ω) are nonresonant, the change in the refractive index follows instantaneously the variation of the intensity of the electromagnetic radiation. Consequently, the carrier frequency and, in the case of free propagation (no waveguiding), the spatial intensity distribution of an intense light pulse are subject to ultrafast modulation (self-phase modulation and time-dependent self-focusing) when propagating through transparent optical media.

© 1992 Optical Society of America