High-SNR 3D dark-field microscopy based on orbital angular momentum extraction

Abstract

A 3D dark-field microscopy with high signal-to-noise ratio (SNR) is realized by demodulating the orbital angular momentum (OAM) information of the compound signal from the sample. Under ordinary Gaussian beam illumination containing pure 0th-order OAM component, the scattering of the sample extends the input light energy to non-zero order ones. In order to extract the specific order of OAM component, a forked-grating hologram with opposite wavefront is applied in the detection path. The SNR with 4.5 times enhancement is observed experimentally compared with conventional dark-field imaging in that the demodulation of the dark-field signal in OAM domain realizes a comparatively more thorough separation of reflected and scattered light. A spatial resolution of better than 0.78 μm is achieved. The 3D sectioning ability inherited from confocal configuration is verified by volumetric imaging of the defects of a fused silica sample with topological charge m = 0, 1, 2. The analysis of multiple orders tends to provide indications for specific characteristics of the samples such as the structural chirality and symmetry.