Dynamic speckle generation tuned by thermo-optic effects

• The temporal fluctuation rate of dynamic speckles is tuned thermo-optically. • A thermo-optical colloidal suspension was engineered near refractive index matching. • Different regimes of volume scattering can be explored as temperature is varied. • Characterization of dynamic speckles in a dedicated optical fiber-based setup. • Tuning of temporal fluctuations rate is demonstrated over one order of magnitude. We present a strategy for the generation of dynamic, random speckles, whose characteristic fluctuation time can be adjusted controllably by tuning the volume scattering properties of a complex medium by means of its geometrical size and thermo-optic effects. We engineered a thermo-optical colloidal suspension, around the condition of refractive index matching between the particles and the suspending medium, that allows experiencing different regimes of volume scattering (null, single, multiple) controllably as temperature is varied. We characterized the temporal fluctuations of dynamic speckles in a dedicated optical fiber-based setup, in transmission, where we placed the thermo-optic colloidal suspension between the facets of two collinear optical fibers; a multimode fiber sets the input, static speckle, and the output, dynamic speckle is collected with a single-mode fiber for its characterization. The characteristic fluctuation time was successfully tuned by one order of magnitude, in the range 10 ms ≤ τ ≤ 100 ms . Because dynamic speckles are generated through the light scattering of Brownian particles, realizations are ensured to be random, statistically independent regardless of the fluctuation rate.