Abstract
In this study, a simple and novel phase-retrieval scheme is implemented using multi-angle illumination to enhance the resolution of lensless microscopy. A random-phase mask (from 0 to 2π) precedes the sample to encode the information at the sensor plane. The sample is illuminated with multiple angles that are symmetrical along the optical axis of the system. The system is initially calibrated while recording the images without any sample at the corresponding multi angles. The two types of image are mutually subtracted, and the resultant images are summed at the sensor plane and backpropagated to the sample plane. The final image is free of the twin-image effect, and has a high signal-to-noise ratio owing to the multi angles of the illumination scheme. This scheme gives a resolution of ~4 micron for a large field-of-view (~15 mm2). The scheme is useful for robust imaging owing to the fast phase-retrieval method, and it enables a straightforward analytical reconstruction instead of using complicated iterative algorithms in a lensless microscopic setup.
Highlights
Microscopic imaging techniques are usually categorized into confocal and wide-field classes based on the field-of-view (FOV)
The first step is the experimental capturing of images at the sensor plane, and the second one is the reconstruction of a resultant image with enhanced resolution and improved signal-to-noise (SNR) ratio
The sample elements scatter coherent light, and the empty space of the sample gives unscattered light, which acts as the reference beam
Summary
Microscopic imaging techniques are usually categorized into confocal and wide-field classes based on the field-of-view (FOV). The recorded image is reconstructed in the sample plane with low resolution owing to the large pixel size and missing higher spatial frequencies. The inverse Fourier transform of the image is obtained to obtain the optical field of the sample This simple reconstruction process encountered several limitations, which are further compensated through alternate approaches to yield high-resolution images. To minimize the effect of twin images in lensless microscopy, the optical component, which is called a phase mask, has been introduced to encode the sample information at the sensor plane[16,17]. The fundamental principle of our mathematical model is based on the phase-masking scheme[16] This model is further coupled with the multi-angle illumination scheme to obtain the high-resolution image. The field at the sample plane is given by Eq (4)
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