Speckle decorrelation in fundamental and second-harmonic light scattered from nonlinear disorder

TL;DR

This study investigates how speckle patterns in nonlinear disordered media decorrelate with increasing incident power, revealing faster decorrelation in second-harmonic light through experiments and a supporting theoretical model.

Contribution

It provides the first detailed analysis of speckle decorrelation in both fundamental and second-harmonic light in nonlinear disordered media, supported by experiments and a new theoretical framework.

Findings

Speckle correlation decreases with increasing power.

Second-harmonic speckle decorrelates faster than fundamental.

Theoretical model explains the physical mechanisms behind decorrelation.

Abstract

Speckle patterns generated in a disordered medium carry a lot of information despite the apparent complete randomness in the intensity pattern. When the medium possesses $\chi^{(2)}$ nonlinearity, the speckle is sensitive to the phase of the incident fundamental light, as well as the light generated within. Here, we examine the speckle decorrelation in the fundamental and second-harmonic transmitted light as a function of varying power in the fundamental beam. At low incident powers, the speckle patterns produced by successive pulses exhibit strong correlations, that decrease with increasing power. The average correlation in the second-harmonic speckle decays faster than in the fundamental speckle. Next, we construct a theoretical model, backed up by numerical computations, to obtain deeper physical insights on the faster decorrelations in the second-harmonic light. Whilst providing excellent qualitative agreement with the experiments, the model sheds important light on the contribution of two effects in the correlations, namely, the generation of second-harmonic light, and the propagation thereof.