InN films with In and N polarities grown by molecular beam epitaxy are studied by photoreflectance (PR). No PR feature is observed at 293 K. At 50 K, for N-polar InN, a broad PR feature with Franz-Keldysh oscillations (FKOs) is observed. The surface electric field (312 kV/cm) and band gap (0.682 eV) are deduced from analyzing FKO extremes. However, some narrow PR features are observed for In-polar InN and three transition energies are obtained, but no FKO is observed. These indicate that the surface electric field (or surface band bending) of In-polar InN is smaller than that of N-polar InN

During the last decades, several resolution enhancement methods for optical microscopy beyond diffraction limit have been developed. Nevertheless, those hardware-based techniques typically require strong illumination, and fail to improve resolution in deep tissue. Here we develop a high-speed computational approach, three-dimensional virtual spatial overlap modulation microscopy (3D-vSPOM), which immediately solves the strong-illumination issue. By amplifying only the spatial frequency component corresponding to the un-scattered point-spread-function at focus, plus 3D nonlinear value selection, 3D-vSPOM shows significant resolution enhancement in deep tissue. Since no iteration is required, 3D-vSPOM is much faster than iterative deconvolution. Compared to non-iterative deconvolution, 3D-vSPOM does not need a priori information of point-spread-function at deep tissue, and provides much better resolution enhancement plus greatly improved noise-immune response. This method is ready to be amalgamated with two-photon microscopy or other laser scanning microscopy to enhance deep-tissue resolution.

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