Two-photon microscopy with enhanced resolution and signal-to-background ratio using hollow Gaussian beam excitation.

Two-photon microscopy (TPM) offers deeper imaging depth inside the scattering medium, however, it suffers from limited resolution owing to the longer excitation wavelength. We demonstrate the use of a hollow Gaussian beam (HGB) at the therapeutic window to improve the resolution and signal-to-background ratio (SBR). The HGB was produced by omitting the azimuthal phase term from the vortex mode, and the excitation point spread function (PSF) can be readily tuned by the mode order.

Polarization modulation for imaging behind the scattering medium.

We propose and experimentally demonstrate a technique, based on polarization modulation, for imaging of the polarization discriminating object hidden behind a scattering medium. This is realized by making use of the relation between the complex correlation function of the randomly scattered orthogonal polarization components in the far field and polarized source structure at the scattering plane. Full use of a polarimetric parameter at the scattering plane is realized in the object plane reconstruction behind the scattering medium using a backpropagation approach.