Wavefront sensing for low-coherent sources through spatial coherence revival

Abstract

An interferometry based wavefront sensing scheme applicable to low-coherent light sources is proposed and demonstrated. Using a pair of cascaded Sagnac interferometers, spatial frequency multiplexed interference of three sheared copies of the wavefront is recorded. The independent vector gradients obtained are used to reconstruct the wavefront. We overcome the spatio-temporal coherence limitations of the light source through the choice of spatial and spectral distribution of the light source. A Gaussian spectral distribution enables the measurement of the phase gradient corresponding to the central wavelength. Introduction of aperture for controlling the spatial distribution of the extended light source, we revive the spatial coherence of the optical field at the detector plane. We revive the spatial coherence of the field for the set value of lateral shear to maintain the visibility of the interference at the detectable level. Validating the scheme through measurement of changes in wavefront as a function of a collimation lens position, we apply it to reconstruct the wavefront of a light beam passing through a pseudo random phase plate, an atmospheric turbulence simulator.