Imaging through complex media

Demonstration of the field of view advantage of conjugate (left) versus pupil (right) AO using 2-photon microscopy.

The imaging performance of an optical microscope can be degraded by sample-induced aberrations. A general strategy to undo the effect of these aberrations is to apply wavefront correction with a deformable mirror (DM). In most cases the DM is placed conjugate to the microscope pupil, called pupil adaptive optics (AO). When the aberrations are spatially variant an alternative configuration involves placing the DM conjugate to the main source of aberrations, called conjugate AO. We have provided a theoretical and experimental comparison of both configurations for the simplified case where spatially variant aberrations are produced by a well-defined phase screen. Conjugate AO is found to provide a significant FOV advantage, which we  xperimentally verified with standard widefield microscopy and with 2-photon microscopy.

We have also implemented a fast closed-loop feedback implementation of AO that requires no guide stars, where the sample itself serves as the reference. Several features of our implementation are new. First, it is based on a high-resolution, single-shot wavefront sensor that is compatible with extended samples. Second, it is applied to widefield (i.e., nonscanning) microscopy in a conjugate AO configuration that increases field of view. Third, it makes use of a fast algorithm to identify sample-induced aberrations using illumination from an arbitrarily shaped source. We present the principle of our technique and proof-of-concept experimental demonstrations.

Finally, we have characterized the spectral decorrelation that arises from the propagation of polychromatic light through complex media.

Demonstration of real-time, closed-loop, conjugate AO using a PAW wavefront sensor. Sample is elastic mouse cartilage.
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