Adaptive Digital Scan Variable Pixels

The square and rectangular shape of the pixels in the digital images for sensing and display purposes introduces several inaccuracies in the representation of digital images. The major disadvantage of square pixel shapes is the inability to accurately capture and display the details in the objects having variable orientations to edges, shapes and regions. This effect can be observed by the inaccurate representation of diagonal edges in low resolution square pixel images. This paper explores a less investigated idea of using variable shaped pixels for improving visual quality of image scans without increasing the square pixel resolution. The proposed adaptive filtering technique reports an improvement in image PSNR.Comment: 4th International Conference on Advances in Computing, Communications and Informatics, August, 201

Sub-pixel Layout for Super-Resolution with Images in the Octic Group

13th European Conference, Zurich, Switzerland, September 6-12, 2014, Proceedings, Part IThis paper presents a novel super-resolution framework by exploring the properties of non-conventional pixel layouts and shapes. We show that recording multiple images, transformed in the octic group, with a sensor of asymmetric sub-pixel layout increases the spatial sampling compared to a conventional sensor with a rectilinear grid of pixels and hence increases the image resolution. We further prove a theoretical bound for achieving well-posed super-resolution with a designated magnification factor w.r.t. the number and distribution of sub-pixels. We also propose strategies for selecting good sub-pixel layouts and effective super-resolution algorithms for our setup. The experimental results validate the proposed theory and solution, which have the potential to guide the future CCD layout design with super-resolution functionality.United States. Air Force (Assistant Secretary of Defense for Research & Engineering Contract #FA8721-05-C-0002)SUTD-MIT International Design Centre (Joint Postdoctoral Programme)Singapore University of Technology and Design (SUTD StartUp Grant ISTD 2011 016)Singapore. Ministry of Education (MOE Academic Research Fund MOE2013-T2-1-159

A Demonstration of Wavefront Sensing and Mirror Phasing from the Image Domain

In astronomy and microscopy, distortions in the wavefront affect the dynamic range of a high contrast imaging system. These aberrations are either imposed by a turbulent medium such as the atmosphere, by static or thermal aberrations in the optical path, or by imperfectly phased subapertures in a segmented mirror. Active and adaptive optics (AO), consisting of a wavefront sensor and a deformable mirror, are employed to address this problem. Nevertheless, the non-common-path between the wavefront sensor and the science camera leads to persistent quasi-static speckles that are difficult to calibrate and which impose a floor on the image contrast. In this paper we present the first experimental demonstration of a novel wavefront sensor requiring only a minor asymmetric obscuration of the pupil, using the science camera itself to detect high order wavefront errors from the speckle pattern produced. We apply this to correct errors imposed on a deformable microelectromechanical (MEMS) segmented mirror in a closed loop, restoring a high quality point spread function (PSF) and residual wavefront errors of order $\sim 10$ nm using 1600 nm light, from a starting point of $\sim 300$ nm in piston and $\sim 0.3$ mrad in tip-tilt. We recommend this as a method for measuring the non-common-path error in AO-equipped ground based telescopes, as well as as an approach to phasing difficult segmented mirrors such as on the \emph{James Webb Space Telescope} primary and as a future direction for extreme adaptive optics.Comment: 9 pages, 6 figure

Improvements to the alignment process in electron-beam lithography

Electron beam lithography is capable of defining structures with sub-10 nm linewidths. To exploit this capability to produce working devices with structures defined in multiple 'lithographic steps' a process of alignment must be used. The conventional method of scanning the electron beam across simple geometrically shaped markers will be shown inherently to limit the alignment accuracy attainable. Improvements to alignment allow precise placement of elements in complex multi-level devices and may be used to realise structures which are significantly smaller than the single exposure resist limit. Correlation based alignment has been used previously as an alignment technique, providing improvements to the attainable accuracy and noise immunity of alignment. It is well known that the marker pattern used in correlation based alignment has a strong influence on the magnitude of the improvements that can be realised. There has, to date, however, been no analytical study of how the design of marker pattern affects the correlation process and hence the alignment accuracy possible. This thesis analyses the correlation process to identify the features of marker patterns that are advantageous for correlation based alignment. Several classes of patterns have been investigated, with a range of metrics used to determine the suitability and performance of each type of pattern. Penrose tilings were selected on this basis as the most appropriate pattern type for use as markers in correlation based alignment. A process for performing correlation based alignment has been implemented on a commercial electron beam lithography tool and the improvements to the alignment accuracy have been demonstrated. A method of measuring alignment accuracy at the nanometer scale, based on the Fourier analysis of inter-digitated grating has been introduced. The improvements in alignment accuracy realised have been used to facilitate the fabrication of 'nanogap' and 'nanowire' devices - structures which have application in the fields of molecular electronics and quantum conduction. Fabrication procedures for such devices are demonstrated and electrical measurements of such structures presented to show that it is a feasible method of fabrication which offers much greater flexibility than the existing methods for creating these devices

Image super-resolution using gradient profile prior

In this paper, we propose an image super-resolution approach using a novel generic image prior – gradient profile prior, which is a parametric prior describing the shape and the sharpness of the image gradients. Using the gradient profile prior learned from a large number of natural images, we can provide a constraint on image gradients when we estimate a hi-resolution image from a low-resolution image. With this simple but very effective prior, we are able to produce state-of-the-art results. The reconstructed hiresolution image is sharp while has rare ringing or jaggy artifacts

Vision and revision: wavefront sensing from the image domain

An ideal telescope with no optical aberrations can achieve a resolution and contrast limited by the wave nature of light, such that the finest detail that can be resolved is of the order of the angle subtended by one wavelength over the diameter of the telescope. For telescopes operating close to this ideal case, however, it is rare that the full performance of the diffraction limit is achieved, as small optical imperfections cause speckles to appear in the image. These are difficult to calibrate, as they are often caused by thermal and mechanical variations in the optical path which vary slowly with time. The quasi-static speckles that they impose can mimic the real signal of a faint star or planet orbiting the primary target, and these therefore impose the principal limitation on the angular resolution and contrast of instruments designed to detect exoplanets and faint companions. These aberrations can be corrected by active optics, where a wavefront sensor is used to used to reconstruct a map of the distortions which can then be compensated for by a deformable mirror, but there is a problem with this also: differrential aberrations between the wavefront sensor and science camera are not detected. In this thesis, I will discuss a successful laboratory implementation of a recently-proposed technique for reconstructing a wavefront map using only the image taken with the science camera, which can be used to calibrate this non-common path error. This approach, known as the asymmetric pupil Fourier wavefront sensor, requires that the pupil not be centrosymmetric, which is easily achieved with a mask, with segment tilting, or with judiciously placed spiders to support the secondary mirror, and represents a promising way forward for characterizing and correcting segment misalignments on future missions such as the James Webb Space Telescope

Transient absorption imaging of hemeprotein in fresh muscle fibers

2022 Summer.Includes bibliographical references.Mitochondrial diseases affect 1 in 4000 individuals in the U.S. among adults and children of all races and genders. Nevertheless, these diseases are hard to diagnose because they affect each person differently. Meanwhile the gold standard diagnosis methods are usually invasive and time- consuming. Therefore, a non-invasive and in-vivo diagnosis method is highly demanded in this area. Our goal is to develop a non-invasive diagnosis method based on the endogenous nonlinear optical effect of the live tissues. Mitochondrial disease is frequently the result of a defective electron transport chain (ETC). Our goal is to develop a non-invasive way to measure redox within the ETC, specifically, of cytochromes. Cytochromes are iron porphyrins that are essential to the ETC. Their redox states can indicate cellular oxygen consumption and mitochondrial ATP production. So being able to differentiate the redox states of cytochromes will offer us a method to characterize mitochondrial function. Meanwhile, Chergui's group found out that the two redox states of cytochrome c have different pump-probe spectroscopic responses, meaning that the transient absorption (TA) decay lifetime can be a potential molecular contrast for cytochrome redox state discrimination. Their research leads us to utilize the pump-probe spectroscopic idea to develop a time-resolved optical microscopic method to differentiate not only cytochromes from other chemical compounds but also reduced cytochromes from oxidized ones. This dissertation describes groundbreaking experiments where transient absorption is used to reveal excited-state lifetime differences between healthy controls and an animal model of mitochondrial disease, in addition to differences between reduced and oxidized ETC in isolated mitochondria and fresh preparations of muscle fibers. For our initial experiments, we built a pump-probe microscopic system with a fiber laser source, producing 530nm pump and 490nm probe using a 3.5kHz laser scanning rate. The pulse durations of pump and probe are both 800fs. For the preliminary results, we have successfully achieved TA decay contrast between reduced and oxidized cytochromes in solution form. Then we have achieved SNR enhanced pump-probe image of BGO crystal particles with the help of the software- based adaptive filter noise canceling method. We also have installed a FPGA-based adaptive filter to enhance the pump-probe signals of the electrophoresis gels that contain different mitochondrial respiratory chain supercomplexes. However, because the noise floor was still 30 dB higher than shot noise limit, cytochrome imaging in live tissues was still problematic. We then built another pump-probe microscope with a solid- state ultrafast laser source. In that way, we do not need to worry about laser relative intensity noise (RIN) anymore, since the noise floor of the solid-state laser source can reach the shot noise limit at MHz region. One other advantage of the new laser source is that it can provide one tunable laser output that can be directly converted to the probe pulse with tunable center wavelength. Its tunability can cover the entire visible spectrum. We realized a pump-probe microscopy with a 520nm pump pulse and a tunable probe pulse. The tunability on the probe arm allows us to explore better pump-probe contrast between two redox states. What's more, I will introduce my preliminary results of utilizing supercontinuum generation in a photonic crystal fiber (PCF) to realize tunability on pump wavelength. In that way, more possibilities will be unlocked. And the hyperspectral pump-probe microscope will be able to distinguish more molecules