Showing papers on "Optical transfer function published in 2021"

Topological optical differentiator

Abstract: Optical computing holds significant promise of information processing with ultrahigh speed and low power consumption. Recent developments in nanophotonic structures have generated renewed interests due to the prospects of performing analog optical computing with compact devices. As one prominent example, spatial differentiation has been demonstrated with nanophotonic structures and directly applied for edge detection in image processing. However, broadband isotropic two-dimensional differentiation, which is required in most imaging processing applications, has not been experimentally demonstrated yet. Here, we establish a connection between two-dimensional optical spatial differentiation and a nontrivial topological charge in the optical transfer function. Based on this connection, we experimentally demonstrate an isotropic two-dimensional differentiation with a broad spectral bandwidth, by using the simplest photonic device, i.e. a single unpatterned interface. Our work indicates that exploiting concepts from topological photonics can lead to new opportunities in optical computing.

Image deconvolution for optical small satellite with deep learning and real-time GPU acceleration

Abstract: In-orbit optical-imaging instruments may suffer from degradations due to space environment impacts or long-time operation. The degradation causes blurring on the image received from the ground. Degradations come from defocus and spherical aberrations cause blurring on the received image. Image deblurring should be done in pre-processing step to compensate the sensor bad impacts. The aberrations are modeled by Zernike polynomials and treated by deep learning in deblurring method. This paper presents a method to deconvolve the acquired data to improve the image quality. A convolution neural network is trained to estimate the point spread function (PSF) parameters using acquired images over satellite calibration site with specific pattern. Image deconvolution is performed to obtain image signal-to-noise (SNR) and modulation transfer function (MTF) improvement. Technical and image data used for modeling and experiment are used from VNREDSat-1 satellite (the first operational Vietnam Earth observation optical small satellite). The experiment is performed on computers accelerated by graphics processing units (GPU) to ensure fast computation.

High Resolution Imaging Camera (HiRIC) on China’s First Mars Exploration Tianwen-1 Mission

Abstract: The High-Resolution Imaging Camera (HiRIC) is one major payload of China’s first Mars exploration mission, and its main objective is to obtain the detailed observation images of the key areas on the Martian surface. In this paper, the leading group of HiRIC shows a full blueprint of the HiRIC. The HiRIC can achieve a high resolution (0.5 m at an altitude of 265 km) with a wide swath width of 9 km. The HiRIC adopts an Off-Axis Three-Mirror Astigmatic (TMA) optical system with a focal length of 4640 mm, an F-number of 12 and a Field of View (FOV) of 2° × 0.693°. In order to reduce the instrument weight, carbon-based material is widely used in the opto-mechanical structure which is in ultra-lightweight design, thus, a light-weight camera with a total mass of 42 kg is obtained. The Time Delay and Integration (TDI) Charge Coupled Devices (CCDs) and Complementary Metal-Oxide-Semiconductor Transistor (CMOS) detectors are all set on the imaging plane to achieve the push-broom imaging and frame imaging, respectively. And the high Signal-to-Noise Ratio (SNR) >100:1 can achieve in multi observation types for various scientific imaging tasks. After 4-year design and fabricate, the HiRIC has been assembly. The testing results show that the instrument is in good condition, and the Modulation Transfer Function (MTF) can achieve 0.18 at Nyquist frequency. The HiRIC can achieve a well image on China first Mars exploration mission.

Depth from Defocus with Learned Optics for Imaging and Occlusion-aware Depth Estimation

Abstract: Monocular depth estimation remains a challenging problem, despite significant advances in neural network architectures that leverage pictorial depth cues alone. Inspired by depth from defocus and emerging point spread function engineering approaches that optimize programmable optics end-to-end with depth estimation networks, we propose a new and improved framework for depth estimation from a single RGB image using a learned phase-coded aperture. Our optimized aperture design uses rotational symmetry constraints for computational efficiency, and we jointly train the optics and the network using an occlusion-aware image formation model that provides more accurate defocus blur at depth discontinuities than previous techniques do. Using this framework and a custom prototype camera, we demonstrate state-of-the art image and depth estimation quality among end-to-end optimized computational cameras in simulation and experiment.

Laplace metasurfaces for optical analog computing based on quasi-bound states in the continuum

Abstract: Laplace operation, the isotropic second-order differentiation, on spatial functions is an essential mathematical calculation in most physical equations and signal processing. Realizing the Laplace operation in a manner of optical analog computing has recently attracted attention, but a compact device with a high spatial resolution is still elusive. Here, we introduce a Laplace metasurface that can perform the Laplace operation for incident light-field patterns. By exciting the quasi-bound state in the continuum, an optical transfer function for nearly perfect isotropic second-order differentiation has been obtained with a spatial resolution of wavelength scale. Such a Laplace metasurface has been numerically validated with both 1D and 2D spatial functions, and the results agree well with that of the ideal Laplace operation. In addition, the edge detection of a concerned object in an image has been demonstrated with the Laplace metasurface. Our results pave the way to the applications of metasurfaces in optical analog computing and image processing.

Holographic pancake optics for thin and lightweight optical see-through augmented reality.

Abstract: Holographic pancake optics have been designed and fabricated in eyewear display optics literature dating back to 1985, however, a see-through pancake optic solution has not been demonstrated to date. The key contribution here is the first full-color volume holographic pancake optic in an optical see-through configuration for applications in mobile augmented reality. Specifically, the full-color volume holographic pancake is combined with a flat lightguide in order to achieve the optical see-through property. The fabricated hardware optics has a measured field of view of 29 degrees (horizontal) by 12 degrees (vertical) and a measured large eyebox that allows a ±10 mm horizontal motion and ∼±3 mm vertical motion for a 4 mm diameter pupil. The measured modulation transfer function (average orientation) is 10% contrast at 10 lp/deg. Three holograms were characterized with respect to their diffraction efficiency, angular bandwidth, focal length, haze, and thickness parameters. The phase function in the reflection mode hologram implements a spherical mirror that has a relatively simple recording geometry.

Optimizing illumination in three-dimensional deconvolution microscopy for accurate refractive index tomography

Abstract: In light transmission microscopy, axial scanning does not directly provide tomographic reconstruction of specimen. Phase deconvolution microscopy can convert a raw intensity image stack into a refractive index tomogram, the intrinsic sample contrast which can be exploited for quantitative morphological analysis. However, this technique is limited by reconstruction artifacts due to unoptimized optical conditions, which leads to a sparse and non-uniform optical transfer function. Here, we propose an optimization method based on simulated annealing to systematically obtain optimal illumination schemes that enable artifact-free deconvolution. The proposed method showed precise tomographic reconstruction of unlabeled biological samples.

Characterization and performance evaluation of the XSPA-500k detector using synchrotron radiation

Abstract: Hybrid photon counting (HPC) detectors are widely used at both synchrotron facilities and in-house laboratories The features of HPC detectors, such as no readout noise, high dynamic range, high frame rate, excellent point spread function, no blurring etc along with fast data acquisition, provide a high-performance detector with a low detection limit and high sensitivity Several HPC detector systems have been developed around the world A number of them are commercially available and used in academia and industry One of the important features of an HPC detector is a fast readout speed Most HPC detectors can easily achieve over 1000 frames s−1, one or two orders of magnitude faster than conventional CCD detectors Nevertheless, advanced scientific challenges require ever faster detectors in order to study dynamical phenomena in matter The XSPA-500k detector can achieve 56 kframes s−1 continuously, without dead-time between frames Using `burst mode', a special mode of the UFXC32k ASIC, the frame rate reaches 1 000 000 frames s−1 XSPA-500k was fully evaluated at the Metrology beamline at Synchrotron SOLEIL (France) and its readout speed was confirmed by tracking the synchrotron bunch time structure The uniformity of response, modulation transfer function, linearity, energy resolution and other performance metrics were also verified either with fluorescence X-rays illuminating the full area of the detector or with the direct beam

Asymmetric Metal-Dielectric Metacylinders and Their Potential Applications From Engineering Scattering Patterns to Spatial Optical Signal Processing

Abstract: We propose a bianisotropic hybrid metal-dielectric structure comprising dielectric and metallic cylindrical wedges wherein the composite metacylinder enables advanced control of electric, magnetic, and magnetoelectric resonances. We establish a theoretical framework in which the electromagnetic response of this meta-atom is described through the electric and magnetic multipole moments. The complete dynamic polarizability tensor, expressed in a compact form, is derived as a function of the Mie-scattering coefficients. Further, the constitutive parameters---determined analytically---illustrate the tunability of the structure's frequency and strength of resonances in light of its high degree of geometric freedom. Flexibility in the design makes the proposed metacylinder a viable candidate for various applications in the microscopic (single meta-atom) and macroscopic (metasurface) levels. We show that the highly versatile bianisotropic meta-atom is amenable to being designed for the desired electromagnetic response, such as electric dipole-free and zero or near-zero (backward and forward) scattering at the microscopic level. In addition, we show that the azimuthal asymmetry gives rise to normal polarizability components, which are vital elements in synthesizing asymmetric optical transfer function at the macroscopic level. We conduct a precise inspection, from the microscopic to the macroscopic level, of the metasurface synthesis for emphasizing on the role of normal polarizability components for spatial optical signal processing. It is shown that this simple two-dimensional asymmetric meta-atom can perform first-order differentiation and edge detection at normal illumination. The results reported herein contribute toward improving the physical understanding of wave interaction with artificial materials composed of asymmetric elongated metal-dielectric inclusions and open the potential of its application in spatial signal and image processing.

Asymmetric self-coherent detection.

Abstract: The bandwidth upgrade required in short-reach optical communications has prompted the need for detection schemes that combine field reconstruction with a cost-effective subsystem architecture. Here we propose an asymmetric self-coherent detection (ASCD) scheme for the field reconstruction of self-coherent (SC) complex double-sideband (DSB) signals based on a direct-detection (DD) receiver with two reception paths. Each reception path consists of a photodiode (PD) and an analog-to-digital converter for the detection of a part of the received optical signal that experiences a different optical transfer function via the configuration of an optical filter. We derive an analytical solution to reconstructing the signal field and show the optimal filter response in optimizing the signal SNR. Further, we numerically characterize the theoretical performance of a specific ASCD scheme based on a chromatic dispersion filter and validate the principle of the ASCD scheme in a proof-of-concept experiment. The ASCD scheme approaches the electrical spectral efficiency of coherent detection with a cost-effective DD receiver, which shows the potential for high-speed short-reach links required by edge cloud communications and mobile X-haul systems.

Isotropic topological second-order spatial differentiator operating in transmission mode

Abstract: Differentiation has widespread applications, particularly in image processing for edge detection. Significant advances have been made in using nanophotonic structures and metamaterials to perform such operations. In particular, a recent work demonstrated a topological differentiator in which the transfer function exhibited a topological charge, making the differentiation operation robust to variations in operating conditions. The demonstrated topological differentiator, however, operates in reflection mode at off-normal incidence and is difficult to integrate into compact imaging systems. In this work, we design a topological differentiator that operates isotropically in transmission mode at normal incidence. The device exhibits an optical transfer function with a symmetry-protected topological charge of ±2 and performs second-order differentiation. Our work points to the potential of harnessing topological concepts for optical computing applications.

High-energy micrometre-scale pixel direct conversion X-ray detector

Abstract: The objective of this work was to fabricate and characterize a new X-ray imaging detector with micrometre-scale pixel dimensions (7.8 µm) and high detection efficiency for hard X-ray energies above 20 keV. A key technology component consists of a monolithic hybrid detector built by direct deposition of an amorphous selenium film on a custom designed CMOS readout integrated circuit. Characterization was carried out at the synchrotron beamline 1-BM-B at the Advanced Photon Source of Argonne National Laboratory. The direct conversion detector demonstrated micrometre-scale spatial resolution with a 63 keV modulation transfer function of 10% at Nyquist frequency. In addition, spatial resolving power down to 8 µm was determined by imaging a transmission bar target at 21 keV. X-ray signal linearity, responsivity and lag were also characterized in the same energy range. Finally, phase contrast edge enhancement was observed in a phase object placed in the beam path. This amorphous selenium/CMOS detector technology can address gaps in commercially available X-ray detectors which limit their usefulness for existing synchrotron applications at energies greater than 50 keV; for example, phase contrast tomography and high-resolution imaging of nanoscale lattice distortions in bulk crystalline materials using Bragg coherent diffraction imaging. The technology will also facilitate the creation of novel synchrotron imaging applications for X-ray energies at or above 20 keV.

Design aspects of large-aperture MODE lenses

Abstract: Design aspects of multiple-order diffraction engineered surface (MODE) lenses are discussed that result in significant improvement of geometrical off-axis performance. A new type of aberration that is characteristic of this type of segmented lens, which is called zonal field shift, is minimized by curving front intercepts of zone transitions. Three MODE designs are compared, based on a 240 mm aperture, 1 m focal length system with a 0.125° half field angle over the astronomical R wavelength band (589 nm to 727 nm). Optimized curved-front designs indicate diffraction-limited monochromatic geometrical performance over the full field of view. A technique is implemented with a combination of a non-sequential ray-trace model and a diffraction code to model physical optical effects, which indicates that the modulation transfer function (MTF) of MODE lenses are significantly improved compared to a first-order equivalent refractive achromat.

Edge-based modulation transfer function measurement method using a variable oversampling ratio.

Abstract: The ISO 12233 edge-based method approximates the modulation transfer function (MTF) as a function of horizontal or vertical spatial frequency by analyzing a 1D supersampled edge gradient obtained from the captured image of a near-vertical or near-horizontal bi-tonal edge, respectively. The method involves the slanted projection of pixels in a square array into a linear array of subpixel-wide bins. It can be modified to accommodate diagonal MTF measurements; however, using a fixed integer oversampling ratio degrades the accuracy and precision of diagonal MTF estimates due to periodic misalignment between the projection paths and the bin array. In this study, an edge-based method—called OMNI-sine—is proposed to counter the misalignment and improve MTF estimates by using a variable oversampling ratio dependent on the slant angle.

DeepRegularizer: Rapid Resolution Enhancement of Tomographic Imaging Using Deep Learning

Abstract: Optical diffraction tomography measures the three-dimensional refractive index map of a specimen and visualizes biochemical phenomena at the nanoscale in a non-destructive manner. One major drawback of optical diffraction tomography is poor axial resolution due to limited access to the three-dimensional optical transfer function. This missing cone problem has been addressed through regularization algorithms that use a priori information, such as non-negativity and sample smoothness. However, the iterative nature of these algorithms and their parameter dependency make real-time visualization impossible. In this article, we propose and experimentally demonstrate a deep neural network, which we term DeepRegularizer, that rapidly improves the resolution of a three-dimensional refractive index map. Trained with pairs of datasets (a raw refractive index tomogram and a resolution-enhanced refractive index tomogram via the iterative total variation algorithm), the three-dimensional U-net-based convolutional neural network learns a transformation between the two tomogram domains. The feasibility and generalizability of our network are demonstrated using bacterial cells and a human leukaemic cell line, and by validating the model across different samples. DeepRegularizer offers more than an order of magnitude faster regularization performance compared to the conventional iterative method. We envision that the proposed data-driven approach can bypass the high time complexity of various image reconstructions in other imaging modalities.

Global Information Transmission Model-Based Multiobjective Image Inversion Restoration Method for Space Diffractive Membrane Imaging Systems

Abstract: Diffractive membrane imaging systems have been an important development trend for high-orbit satellite cameras owing to their advantages of large aperture, light weight, rapid manufacture, and low cost. However, caused by the cross-coupling effects of diffraction imaging, membrane properties, subaperture stitching, on-orbit disturbances, and other physical factors, lager-aperture space diffractive membrane imaging systems have specific and complex degradation characteristics: the modulation transfer function (MTF) and signal-to-noise ratio (SNR) have more prominent degradation and serious space-variant characteristics over fields of view, with obvious background radiation properties that seriously affect the application of imaging products. To address this problem, this study established a global information transmission model by characterizing the PSF and background radiation in a full field of view to represent the imaging law of an on-orbit system. Aiming at the inverse problem of the information transmission model, we also propose a novel image inversion restoration method for the special degradation characteristics. In particular, the effect of diffraction efficiency is introduced into the inversion restoration method to solve the background radiation problem. Moreover, we innovatively designed matrix regularization parameters to further improve the correction ability of spatial variation. When the diffraction efficiency was experimentally higher than 60% and the mean measured spatial variability was less than 0.2, the proposed method exhibited a satisfactory processing performance, and could improve multiobjective comprehensive processing, such as transfer function compensation, spatial variation correction, and background radiation removal.

End-to-end learned single lens design using fast differentiable ray tracing.

Abstract: In traditional imaging system design, the optical lens is often optimized toward the artificial optimization target like modulation transfer function and field-of-view (FoV). This usually leads to complex stacks of lenses. In order to reduce the complexity, we propose an end-to-end single lens imaging system design method. First, the imaging and processing model is established, whose input end is the ground truth image, and the output end is the restored image by Res-Unet. Then, with the optimization target of minimizing the difference between the restored image and the ground truth image, the parameters of the lens surface and the parameters of the restoration algorithm are optimized simultaneously by deep learning. In order to realize the end-to-end design, the imaging model is required to be differentiable to the lens parameters, so a fast differentiable ray tracing model is proposed. A single lens imaging system with high-quality large FoV (47°) has been designed by the end-to-end method. This method will have a wide application prospects in the design of light and small optoelectronic imaging systems.

Simulation of anisoplanatic lucky look imaging and statistics through optical turbulence using numerical wave propagation.

Abstract: This paper investigates anisoplanatic numerical wave simulation in the context of lucky look imaging. We demonstrate that numerical wave propagation can produce root mean square (RMS) wavefront distributions and probability of lucky look (PLL) statistics that are consistent with Kolmogorov theory. However, the simulated RMS statistics are sensitive to the sampling parameters used in the propagation window. To address this, we propose and validate a new sample spacing rule based on the point source bandwidth used in the propagation and the level of atmospheric turbulence. We use the tuned simulator to parameterize the wavefront RMS probability density function as a function of turbulence strength. The fully parameterized RMS distribution model is used to provide a way to accurately predict the PLL for a range of turbulence strengths. We also propose and validate a new parametric average lucky look optical transfer function (OTF) model that could be used to aid in image restoration. Our OTF model blends the theoretical diffraction-limited OTF and the average turbulence short exposure OTF. Finally, we show simulated images for several anisoplanatic imaging scenarios that reveal the spatially varying nature of the RMS values impacting local image quality.

Design of a compact dual-channel panoramic annular lens with a large aperture and high resolution.

Abstract: We propose a compact dual-channel panoramic annular lens (PAL) with a large aperture and high resolution to solve three major shortcomings of conventional PAL systems: resolution, imaging quality, and compactness. Using polarization technology, the system integrates two optical channels to eliminate the central blind area. Using our PAL aperture ray-tracing model, the large aperture PAL system with a low F-number of 2.5 and a diameter ratio of 1.5 is realized. The field of view (FoV) of the front channel is 360∘×(0∘−45∘), and the FoV of the side channel is 360∘×(45∘−100∘). Both channels apply Q-type aspheres. The Airy radii of the front channel and the side channel are 1.801 and 1.798 µm, respectively. It indicates that they match the 1.8 µm pixel sensor and can form a great image on the same sensor. The modulation transfer function at 157 lp/mm is greater than 0.4 over the entire FoV. The F-θ distortion is less than 5%, and the relative illuminance is higher than 0.78 in the two channels. The excellent imaging results prove the feasibility of our PAL design method and the advantages of the compact dual-channel PAL system for space-constrained scenes.

MTF improvement for optical synthetic aperture system via mid-frequency compensation

Abstract: Optical synthetic aperture imaging system has grown out the quest for higher angular resolution in astronomy, which combines the radiation from several small sub-apertures to obtain a resolution equivalent to that of a single filled aperture. Due to the discrete distribution of the sub-apertures, pupil function is no longer a connected domain, which further leads to the attenuation or loss of the mid-frequency modulation transfer function (MTF). The mid-frequency MTF compensation is therefore a key focus. In this paper, a complete mid-frequency compensation algorithm is proposed, which can extract and fuse the frequency of different synthetic aperture systems and monolithic aperture systems according to their special MTF characteristics. The dimensions of the monolithic aperture and optical synthetic aperture system are derived, and the longest baseline of the monolithic aperture is much smaller than that of the optical synthetic aperture system. Then the separated spatial frequency information is extracted and synthesized according to the spatial frequency equivalence point. Finally, the full-frequency enhanced image is recovered by using improved Wiener-Helstrom filter, which adopts specific parameters based on different sub-aperture arrangements. The mid-frequency MTF of Golay-3 increases from 0.12 to 0.16 and that of Golay-6 increases from 0.06 to 0.18. Both the simulation and experiment prove that the proposed method not only realizes the spatial resolution determined by the longest baseline of the optical synthetic aperture system, but also successfully compensates its mid-frequency MTF.

3D super-resolution microscopy based on nonlinear gradient descent structured illumination

Abstract: Three-dimensional structured illumination microscopy (3D-SIM) is an essential tool for volumetric fluorescence imaging, which improves both axial and lateral resolution by down-modulating high-frequency information of the sample into the passband of optical transfer function (OTF). And when combining with the 4Pi structure, the performance of 3D-SIM can be further improved. The reconstruction results of generally used linear 3D algorithm, however, are lack of high-fidelity and proneess to generate artifacts. In this paper, we proposed a novel iterative algorithm based on gradient descent combined with a nonlinear optimizer, which can be applied to all 3D-SIM setups (including I5S setup). We verified through simulation that the proposed solution, termed as nonlinear gradient descent structured illumination microscopy (NGD-SIM), achieves more fidelity results which can reach the limitation of theoretical resolution improvement of SIM. Moreover, it can be firmly validated on simulation that this algorithm can effectively reduce the amount of raw data in the case of sinusoidal-pattern illumination, i.e., the algorithm doesn’t need five-step phase shifting; data with any number of phases can theoretically be reconstructed. Our method also provides the possibility to extend the application of sinusoidal-pattern illumination to any kind of interference fringe, which is generated by diversified types of illumination mode.

Power-balanced hybrid optics boosted design for achromatic extended depth-of-field imaging via optimized mixed OTF.

Abstract: A power-balanced hybrid optical imaging system has a diffractive computational camera, introduced in this paper, with image formation by a refractive lens and multilevel phase mask (MPM). This system provides a long focal depth with low chromatic aberrations thanks to MPM and a high energy light concentration due to the refractive lens. We introduce the concept of optical power balance between the lens and MPM, which controls the contribution of each element to modulate the incoming light. Additional features of our MPM design are the inclusion of the quantization of the MPM’s shape on the number of levels and the Fresnel order (thickness) using a smoothing function. To optimize the optical power balance as well as the MPM, we built a fully differentiable image formation model for joint optimization of optical and imaging parameters for the proposed camera using neural network techniques. We also optimized a single Wiener-like optical transfer function (OTF) invariant to depth to reconstruct a sharp image. We numerically and experimentally compare the designed system with its counterparts, lensless and just-lens optical systems, for the visible wavelength interval (400–700) nm and the depth-of-field range (0.5-∞ m for numerical and 0.5–2 m for experimental). We believe the attained results demonstrate that the proposed system equipped with the optimal OTF overcomes its counterparts––even when they are used with optimized OTF––in terms of the reconstruction quality for off-focus distances. The simulation results also reveal that optimizing the optical power balance, Fresnel order, and the number of levels parameters are essential for system performance attaining an improvement of up to 5 dB of PSNR using the optimized OTF compared to its counterpart lensless setup.

Design and Optimization for Mounting Primary Mirror with Reduced Sensitivity to Temperature Change in an Aerial Optoelectronic Sensor

Abstract: In order to improve the image quality of the aerial optoelectronic sensor over a wide range of temperature changes, high thermal adaptability of the primary mirror as the critical components is considered. Integrated optomechanical analysis and optimization for mounting primary mirrors are carried out. The mirror surface shape error caused by uniform temperature decrease was treated as the objective function, and the fundamental frequency of the mirror assembly and the surface shape error caused by gravity parallel or vertical to the optical axis are taken as the constraints. A detailed size optimization is conducted to optimize its dimension parameters. Sensitivities of the optical system performance with respect to the size parameters are further evaluated. The configuration of the primary mirror and the flexure are obtained. The simulated optimization results show that the size parameters differently affect the optical performance and which factors are the key. The mirror surface shape error under 30 °C uniform temperature decrease effectively decreased from 26.5 nm to 11.6 nm, despite the weight of the primary mirror assembly increases by 0.3 kg. Compared to the initial design, the value of the system’s modulation transfer function (0° field angle) is improved from 0.15 to 0.21. Namely, the optical performance of the camera under thermal load has been enhanced and thermal adaptability of the primary mirror has been obviously reinforced after optimization. Based on the optimized results, a prototype of the primary mirror assembly is manufactured and assembled. A ground thermal test was conducted to verify difference in imaging quality at room and low temperature, respectively. The image quality of the camera meets the requirements of the index despite degrading.

Extended DoF and achromatic inverse imaging for lens and lensless MPM camera based on Wiener filtering of defocused OTFs

Abstract: Optimal optical transfer function (OTF) is proposed for RGB inverse imaging with extended depth of field (DoF) and diminished color aberrations. This optimal OTF is derived as the Wiener filter of broadband defocused OTFs. The performance of this new inverse imaging is demonstrated for optical setups with lens and lensless with a multilevel phase mask instead of the lens. The later lensless system designed for the wavelength range (400 to 700) nm and DoF range (0.5 to 1000) m demonstrates the best performance.

Overview of S(T)EM electron detectors with garnet scintillators: Some potentials and limits

Abstract: The paper is focused on a complete configuration and design of a scintillation electron detector in scanning electron and/or scanning transmission electron microscopes (S(T)EM) with garnet scintillators. All processes related to the scintillator and light guide were analyzed. In more detail, excitation electron trajectories and absorbed energy distributions, efficiencies and kinetics of scintillators, as well as the influence of their anti-charging coatings and their substrates, assigned optical properties, and light guide efficiencies of different configurations were presented and discussed. The results indicate problems with low-energy detection below 1 keV when the scandium conductive coating with a thickness of only 3 nm must be used to allow electron penetration without significant losses. It was shown that the short rise and decay time and low afterglow of LuGdGaAG:Ce liquid-phase epitaxy garnet film scintillators guarantee a strong modulation transfer function of the entire imaging system resulting in a contrast transfer ability up to 0.6 lp/pixel. Small film scintillator thicknesses were found to be an advantage due to the low signal self-absorption. The optical absorption coefficients, refractive indices, and the mirror optical reflectance of materials involved in the light transport to the photomultiplier tube photocathode were investigated. The computer-optimized design SCIUNI application was used to configure the optimized light guide system. It was shown that nonoptimized edge-guided systems possess very poor light guiding efficiency as low as 1%, while even very complex optimized ones can achieve more than 20%.

Image Motion Measurement and Image Restoration System Based on an Inertial Reference Laser.

Abstract: Satellites have many high-, medium-, and low-frequency micro vibration sources that lead to the optical axis jitter of the optical load and subsequently degrade the remote sensing image quality. To address this problem, this paper developed an image motion detection and restoration method based on an inertial reference laser, and describe edits principle and key components. To verify the feasibility and performance of this method, this paper also built an image motion measurement and restoration system based on an inertial reference laser, which comprised a camera (including the inertial reference laser unit and a Hartmann wavefront sensor), an integrating sphere, a simulated image target, a parallel light pope, a vibration isolation platform, a vibration generator, and a 6 degrees of freedom platform. The image restoration principle was also described. The background noise in the experiment environment was measured, and an image motion measurement accuracy experiment was performed. Verification experiments of image restoration were also conducted under various working conditions. The experiment results showed that the error of image motion detection based on the inertial reference laser was less than 0.12 pixels (root mean square). By using image motion data to improve image quality, the modulation transfer function (MTF) of the restored image was increased to 1.61–1.88 times that of the original image MTF. The image motion data could be used as feedback to the fast steering mirror to compensate for the satellite jitter in real time and to directly obtain high-quality images.