Fluidic lenses allow for varifocal optical elements, but current approaches are limited by the speed at which focal length can be changed. Here we demonstrate the use of a tunable acoustic gradient (TAG) index of refraction lens as a fast varifocal element. The optical power of the TAG lens varies continuously, allowing for rapid selection and modification of the effective focal length at time scales of 1 mus and shorter. The wavefront curvature applied to the incident light is experimentally quantified as a function of time, and single-frame imaging is demonstrated. Results indicate that the TAG lens can successfully be employed to perform high-rate imaging at multiple locations.

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International audienceUltrafast subpicosecond laser exposure usually induces negative refractive index changes in optical glasses with strong thermal expansion such as borosilicate BK7 due to volume expansion and mechanical rarefaction. We show that temporally shaped laser excitation on picosecond scales and at high repetition rates can invert the regular material response resulting in a significant refractive index increase. Simulations of pulse propagation and evolution of heat and strain waves in BK7 glass exposed to different pulse durations were performed to understand mechanisms of refractive index increase. Narrow spatial distribution of energy for optimized picosecond pulses determines shock-induced plastic deformations accompanied by partial healing of the lateral strain due to preferential heat flow. The matter momentum relaxation produces directional on-axis material compaction