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Optical Engineering
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Item type:Publication, High resolution lensless microscopy based on Fresnel propagation(Society of Photo‑Optical Instrumentation Engineers (SPIE), 2024-07-12); ; Digital holography allows for the recording and reconstruction of three-dimensional images using interference and diffraction principles. The propagation of light from the hologram plane to the reconstruction plane is a crucial step, often achieved through Fresnel propagation, a method that inherently transforms the reconstructed pixel pitch to provide diffraction-limited imaging. However, the accuracy of this method is limited by the Fresnel approximation, especially in applications such as digital holographic microscopy. We present a simple method that significantly improves the accuracy of the Fresnel approximation by incorporating higher orders of the binomial approximation. We validate the effectiveness of our approach through high numerical aperture simulations and experimental results, demonstrating superior sub-micron resolution and reduced distortions compared with standard Fresnel propagation.journal articleBand:63Heft:11201 159 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Characterization of terahertz wavefront aberrations using computational shear-interferometry(Society of Photo‑Optical Instrumentation Engineers (SPIE), 2022-11-10); ; ; ; We propose a new solution for sensing a terahertz (THz) wavefront based on a THz reference-less shear interferometer. The key component of the experimental configuration of the proposed interferometer is a THz Ronchi phase grating (RPG). The RPG is custom designed and fabricated for a 0.28 THz source using mechanical milling on a block of high-density polyethylene with a computer numerical control machine. It acts as a shearing element that generates two diffraction orders, thereby, creating two laterally shifted copies of the investigated wavefront in the sensor plane where a THz camera is placed. The direction of the shear can be varied by rotating the grating. Since the grating is a phase grating, the diffraction efficiency is very high. The approach is verified experimentally by demonstrating interferograms of a spherical wave and wavefront reconstruction from five different shears using a gradient-based iterative process.journal articleBand:61Heft:1137 59