Multiplexed wavefront sensing with a thin diffuser

Abstract

In astronomy or biological imaging, refractive index inhomogeneities of, e.g., atmosphere or tissues, induce optical aberrations that degrade the desired information hidden behind the medium. A standard approach consists of measuring these aberrations with a wavefront sensor (e.g., Shack–Hartmann) located in the pupil plane, and compensating for them either digitally or by adaptive optics with a wavefront shaper. However, in its usual implementation this strategy can only extract aberrations within a single isoplanatic patch, i.e., a region where the aberrations remain correlated. This limitation severely reduces the effective field-of-view in which the correction can be performed. Here, we propose a wavefront sensing method capable of measuring, in a single shot, various pupil aberrations corresponding to multiple isoplanatic patches. The method, based on a thin diffuser (i.e., a random phase mask), exploits the dissimilarity between different speckle regions to multiplex several wavefronts incoming from various incidence angles. We present proof-of-concept experiments carried out in widefield fluorescence microscopy. A digital deconvolution procedure in each isoplanatic patch yields accurate aberration correction within an extended field-of-view. This approach is of interest for adaptive optics applications as well as diffractive optical tomography.