Random dynamic interferometer: Cavity amplified speckle spectroscopy using a highly symmetric coherent field created inside a closed Lambertian optical cavity

A new kind of interferometry is presented, based on the maximal disorder of a single-frequency laser light coherently resonating inside a closed cavity with diffuse reflective walls. After thousands of Lambertian reflections, the optical field at any point inside the cavity is the coherent superposition of a huge number of modes that individually and independently obey a single probability distribution, which is invariant by rotations and translations regardless of the cavity geometry. The resulting interference speckle field has the same statistical properties and exhibits extreme sensitivity to phase fluctuations. From speckle intensity fluctuations, we can measure the various causes that perturb light propagation, be it deformations of the cavity, dynamic scattering of the propagation medium, or fluctuations of the input light phase. Preliminary experiments indicate that strains down to 10^-10 can be detected, that correspond to picometer cavity deformations. This concept of "scrambled" interferometer opens new possibilities in the field of accelerometry or vibrometry, as well as for the enhancement of dynamic or multiple light scattering techniques.