Experimental Progress in Cascading Nonlinear Optics

Abstract

Cascading refers to phenomena associated with the multiple interchange of photons between beams which interact parametrically via second order nonlinearities. [1] Although second harmonic generation (SHG) is the most common example, it also involves sum and difference frequency mixing, optical parametric amplification etc. It has been known since the early days of nonlinear optics that two successive second order interactions can contribute to a third order nonlinearity via χ(2)ijkχ(2)kmn ➔χ(2)ijmn(effective) [2,3] We have found that the effects are more subtle than this and they can give rise to many interesting effects in nonlinear optics. They are essentially of two types, one based on the nonlinear phase shift accumulated by the fundamental beam on transmission through a second order medium and the second is a consequence of the strong coupling which occurs at high intensities between the fundamental and harmonic beams. The second leads to the generation of spatial solitary waves. [4] Here we discuss our progress in studying these effects.