Experimental observation of speckle instability in a two-dimensional disordered medium

Temporal fluctuations of the speckle pattern formed upon backscattering of a laser beam from an interface between gold and nonlinear polymer film have been observed as a function of optical power. The instability can be explained by coupling of laser light to surface plasmons and other guided modes, which experience multiple scattering while propagating in the film along the interface. The speckle pattern produced in this process is extremely sensitive to fluctuations of the scattering potential near the interface.

Research highlights▶ Speckle patterns are extremely sensitive to the interface properties. ▶ We explore speckle instability upon reflection from polydiacetylene coated gold surface. ▶ The instability can be explained by coupling of light to surface plasmons and other guided modes. ▶ Nonlinear effects induce temporal instability of the speckle pattern.