Optical coherence tomography (OCT) is a new imaging technique for observing biological tissue structure. Polarization-sensitive optical coherence tomography (PS-OCT) is a functional extension of OCT, which uses polarized light to probe the sample and extract the polarization properties by detecting the change of the polarization state. In the practical application environment, the optical characteristics of biological samples and the instability of the system will reduce the contrast of the image. Traditional contrast enhancement methods are mostly based on histogram equalization and histogram matching to improve the global quality, which causes the loss of some details of the image and the excessive enhancement of noise. To solve this problem, a local contrast enhancement method is proposed in this paper. The target region and the background region are processed differently by threshold segmentation to enhance the contrast of the signal region and restrain the excessive enhancement of the background noise at the same time. The experimental results showed that this method can enhance the contrast of PS-OCT images and improve the image quality effectively. We believe that this method may play an important role in the application of PS-OCT technology in clinical research.
Polarization aberration of projection optics should be measured, controlled and compensated accurately in high numericalaperture image optical system, such as lithography tools for technical node of 14-5 nm. In this paper, we develop a threestep eigenvalue calibration method for polarization aberration measurement in-situ accurately. The whole system and subsystems can be calibrated by using the wide-view-angle quarter-wave plate as one of the reference samples. In addition, an experimental tool is developed to implement the proposed method, which is of significant importance to quantify and improve the properties of the projection optics in lithography.
The resolution and the field-of-view (FOV) of the Mueller microscope are mutually limiting. The increasing magnification exponentially reduces the FOV of microscopic images, which hinders the acquisition of high-resolution Mueller polarization images with large FOV. To address this problem, we propose a scanning splice method for the Mueller microscope. In this method, an optimized image stitching arithmetic, which specially restricts the selection of feature points to ensure the consistency of stitching results of multiple groups of images with the same position and different polarization states, is combined with Mueller polarization detection techniques. In addition, the combination involved can correct the slight jitter error of the system caused by the rotation of the wave plate during Mueller polarization detection. The experiment results demonstrate that this optimized arithmetic is more accurate than the traditional image stitching arithmetic. This research provides the possibility of the development of the whole slide scanning Mueller microscope.
An efficient method that allows spectral calibration for a Stokes polarimeter is presented in this paper. The calibration procedure only uses a reference polarizer to generate an arbitrary linear polarization state. The reference polarizer could also be calibrated while calibrating the Stokes polarimeter. In addition, this method does not involve the small-angle approximation and could avoid the influence of the initial azimuth error of the retarder and the reference polarizer. The experiment was carried out by a spectroscopy and a polarization state analyzer with a rotating wave plate. Experimental results show that the alignments of axis as well as the true retardation at a specific wavelength of the retarder are obtained.
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