Theory of second-harmonic generation in strongly scattering media

Abstract

Second-harmonic generation is studied in a medium which is both nonlinear and disordered.Disorder-induced strong elastic scattering of both a fundamental and second-harmonic light gives rise to a diffusionlike regime of light propagation. The interference eftects, which cannot be described by the di8'usion approximation, are taken into account. They are shown to lead to a sharp peak in the angular distribution of second-harmonic intensity. The direction of the maximum second-harmonic intensity is found to be roughly opposite to the one determined by the usual phase-matching condition in an e8'ective transparent medium. DifFerent models of disorder are considered, and the corresponding values of peak-to-background ratio are calculated.

Sharpening of enhanced backscattering peak in a disordered gain medium

“…Recently, several authors started to address the issue of what would happen in the nonlinear optical regime. In particular, Kravtsov, Agranovich, and Grigorishin 7 showed that in the case of secondharmonic generation ͑due to 2 nonlinear susceptibility 8 ͒ the EBS peak height for second-harmonic light is very much reduced from the usual factor of 2, due to the restriction that only second-harmonic light generated near the sample surface contributes to the EBS signal, whereas those generated anywhere in the bulk contribute to the diffuse background. Later Agranovich and Kravtsov 9 predicted that when the 3 nonlinear susceptibility 8 is taken into account, the EBS peak function of linear optics must be modified by the appearance of a narrow ''dip'' very close to the backscattering direction, although this result has recently been challenged by Heiderich, Maynard, and van Tiggelen.…”

Second harmonic generation in suspensions of spherical particles

“…This problem has been studied in nonlinear media with cubic nonlinearity (Kerr effect) and proved to be a nontrivial one [6,7]. On the other hand, the lowest-order nonlinear effects -those quadratic in the wave field -have also been considered in the limit l * << l NL [8]. Recent theoretical [9,10] and experimental [11] work suggests that even the simplest realization of a nonlinear disordered medium, a dilute suspension of spherical particles, exhibits a rather unexpected and nontrivial behavior: second harmonic (SH) is generated by a single spherical particle despite its central symmetry and seemingly prohibited second-order nonlinear effects, and a measurable SH signal can be obtained from a dilute suspension of such particles in a single scattering regime [11].…”

Quantitative Measurements of Multilayer Physical Adsorption on Heterogeneous Surfaces from Nonlinear Light Scattering

“…The satisfaction of this requirement in a given experiment ensures a simple quadratic dependence of I 2v on molecular density. Theoretical work has begun to address wave vector matching in complex environments such as glasses [12] and porous media [13]. We take the wave vector matching condition to be satisfied in our samples, as predicted by theory for films thinner than the elastic scattering length for v and 2v photons [13], and confirmed a posteriori by the resulting fits to the data, which are based on a quadratic density dependence.…”