Spatial-domain filter enhanced subtraction microscopy and application to mid-IR imaging

Far-field super-resolution chemical microscopy

Far-field chemical microscopy providing molecular electronic or vibrational fingerprint information opens a new window for the study of three-dimensional biological, material, and chemical systems. Chemical microscopy provides a nondestructive way of chemical identification without exterior labels. However, the diffraction limit of optics hindered it from discovering more details under the resolution limit. Recent development of super-resolution techniques gives enlightenment to open this door behind far-field chemical microscopy. Here, we review recent advances that have pushed the boundary of far-field chemical microscopy in terms of spatial resolution. We further highlight applications in biomedical research, material characterization, environmental study, cultural heritage conservation, and integrated chip inspection.

Terahertz Spiral Spatial Filtering Imaging

In this paper, we propose a terahertz (THz) spiral spatial filtering (SSF) imaging method that can enable image contrast enhancement. The related theory includes three main steps: (1) the THz image of the target is Fourier transformed to the spatial spectrum distribution; (2) the spatial spectrum is modulated by a spiral phase at the Fourier plane; (3) the filtered spatial spectrum is inverse Fourier transformed to the desired THz image. Meanwhile, analytic expression of the final THz image is derived. Due to the unique nature of the spiral phase, THz image contrast enhancement can be achieved and verified by various simulated target images with different contrasts. In our designed THz SSF imaging system, Fourier transform is carried out by the lens, and the spiral phase is acquired by the spiral phase plate (SPP). Proof-of-principle experiments with three different types of targets (carved metal letters, a high-density polyethylene (HDPE) piece with a scratch, and a leaf) were carried out, and the effectiveness of contrast enhancement and edge extraction on the THz reconstruction images was validated.

Label-free superresolution effect of nonlinear reverse saturation absorption thin films through difference method

Label-free superresolution effect of nonlinear reverse saturation absorption (NRSA) thin films was investigated through difference method, where a subdiffraction-limit spot signal was constructed by intensity subtraction of two spots obtained under different laser intensities. By using annealed InSb films as the NRSA thin films, we experimentally obtained the subdiffraction-limit spot signal, and the optimal reduction ratio was approximately 52.5% of the original spot. Experimental results agreed well with theoretical simulations. The simulation results of a 9-point array sample showed the capability to achieve nonfluorescence superresolution imaging using the NRSA effect.