WSe 2 Interdigitated p‐n Homojunction for Broadband High‐Performance Imaging Detection through Localization Effect Synergizes

The remote sensing system engineering process often makes use of modeling and simulation tools to flow down specifications to subsystems and components, and/or to predict performance given a particular set of defined capabilities. A persistent question in the development and use of such tools is that of appropriate level of fidelity. In this paper we look at one problem area encountered in the simulation of panchromatic and other broadband imaging systems, that of accounting for spectrally varying resolution over the band. An established method for treating this variation is that of the polychromatic optical transfer function (OTF), but this technique imposes a measure of complexity on the simulation tool software architecture, as well as on users who must subsequently interact with it. We present a methodology for assessing the required level of fidelity for this problem and show that under some conditions it appears possible to forgo the polychromatic OTF formalism, or else to treat it with less than full rigor, with minimal loss in accuracy.

The Mg 2 Si/4H‐SiC heterojunction was prepared by radio frequency (RF) magnetron sputtering technique. The binding energies of Mg 2p, Si 2p, and C 1s core levels and the maxima of valence band were measured by X‐ray photoelectron spectroscopy (XPS). Using the optical bandgap of Mg 2 Si (0.78 eV) and 4H‐SiC (3.25 eV), the band offsets of valence band (VBO) and conduction band (CBO) at Mg 2 Si/4H‐SiC interface were identified as 1.47 and 1.00 eV, respectively. The band alignment was evaluated to be type‐I band alignment. The Mg 2 Si/4H‐SiC heterojunction could be a promising candidate for the infrared (IR) photodetector.

In a broadband imaging system, the spectral information from the scene can be as important as the spatial information for the task of discriminating an object or feature of interest (the target) from a backdrop of other objects or features of lesser interest (the background) in the image of the scene. A useful measure of the ability to discriminate a target from its background is the apparent contrast between it and the background. The more diverse the scene is, the greater the apparent contrast can be between objects within the spectral passband of the imager. In broadband imaging, the net spectrally and spatially integrated radiances from a target and its background determine the apparent contrast, which in the reflective bands is a function of the spectra of the target and background reflectivities and the scene illumination. The impact of the scene illumination spectrum on apparent contrast can be significant to the point that a given target will be highly visible against a given background under one illumination source and yet hardly visible under a different source of illumination. This paper examines the impact of the spectral natures of the target, background, and the illumination on intrinsic Michelson contrast and target discrimination with notional reflective broadband imaging systems.

The technique commonly used for the analysis of data from broad-band X-ray imaging systems for plasma diagnostics is the filter ratio method. This requires the use of two or more broad-band filters to derive temperatures and line-of-sight emission integrals or emission measure distributions as a function of temperature. Here we propose an alternative analytical approach in which the temperature response of the imaging system is matched to some physical parameter which the experimenter wishes to investigate. We have calculated the temperature response of a system designed to measure the total radiated power along the line of sight of any coronal structure. Other examples are discussed.

Herein, we investigate structural and electronic properties of β-Ga2O3 and p-type Ni-doped α-GaCrO3 (α-GaCrO3:Ni) heterostructure, focusing on its potential for charge separation and rectification mechanisms. Thin films are grown using the magnetron sputtering technique. Synchrotron-based high-resolution x-ray diffraction and high-resolution transmission electron microscopy reveals a sharp and high-quality interface between β-Ga2O3/α-GaCrO3:Ni/Al2O3 epitaxial layers and also confirm single-crystal epitaxial growth of monoclinic (−201) β-Ga2O3 along the [0001] direction of α-GaCrO3:Ni. Optical measurements confirm an average transmission of more than 70% for all thin film samples, showing their potential for transparent optoelectronic devices. Using synchrotron-based photoelectron spectroscopy, valence band offset and conduction band offset at β-Ga2O3/α-GaCrO3:Ni interface are determined to be 2.44 ± 0.2 and 1.44 ± 0.2 eV, respectively, which confirms a type II (staggered gap) energy band alignment at the heterojunction. This type of band alignment is highly useful in a wide range of photovoltaic and optoelectronic devices where efficient charge separation, reduced recombination, and rectification of charge carriers play an important role, such as in solar cells, UV photodetectors, and many other optoelectronic devices.

Broadband imaging systems that contain holographic lenses can be lightweight and have large apertures. We report a Fresnel diffraction analysis of an imaging system that consists of three lenses of arbitrary dispersion. A general solution is found for the wavelength dependence of the lenses to simultaneously correct the imaging system for both longitudinal and lateral paraxial chromatic aberration. As a special case, we describe an optical system that uses holographic lenses to produce a well-corrected image in broadband light. Experimental results that demonstrate the system performance in both laser and broadband illumination are reported.

Existing laser active imaging detection methods are limited by the detection mechanism, which can only capture the intensity image and distance image of the target, and lack practical detection solutions for acquiring images of the target motion state characteristics (non-macroscopic centroid motion, such as rotation, rolling, and other motion characteristics around the centroid). In this paper, a detection method using Geiger mode avalanche photodiode (GM-APD) array detector for heterodyne imaging to obtain images of the target motion state is proposed. An innovative method based on photon counting time interval calculation (PCTIC) is proposed to obtain the Doppler frequency shift of the target echo for each GM-APD pixel, which effectively eliminates useless data unrelated to the signal. With limited data storage and processing speed, the heterodyne imaging performance has been effectively improved to achieve high-precision heterodyne imaging detection of very weak target echoes and to support heterodyne imaging detection of large arrays with more image pixels in parallel. Experiments show that the method can achieve video-level detection at an imaging resolution of 32×32, and with a paucity of echo photons (detection probability of echo is 0.0032), a millimetre-level velocimetry measurement error can be achieved by accumulating only 6 echo photons per image element. The system also shows good resistance to turbulence interference, with target motion state characteristics detected based on velocity images remaining virtually unaffected under turbulence conditions caused by strong flames. This advancement is crucial for target detection in complex working environments such as smart manufacturing and autonomous driving.

Herein, we report epitaxial growth of p-type Ni doped gallium chromium oxide thin film on Al2O3 substrates and studied its band alignment properties with that of the substrate. Thin films are grown using the magnetron-sputtering technique. Synchrotron-based XRD measurements, performed in the coplanar and non-coplanar geometries, confirm high-quality single domain epitaxial growth of p-type α-GaCrO3:Ni. Pendellosung oscillations around the Bragg peak and transmission electron microscopy reveal the high interfacial quality of p-type α-GaCrO3:Ni films with the substrate. Thin film, thickness ∼200 nm, shows around 70% average transmission. The values of valence band and conduction band offsets are determined to be 2.79 ± 0.2 and 0.51 ± 0.2 eV, respectively, which confirm straddling gap band alignment at the heterojunction. This type of alignment creates a threshold barrier for the selective charge carriers and is useful in enhancing the performance of a wide range of devices, including UV photodetectors, metal oxide semiconductor high electron mobility transistors, and light emitters.

In many imaging applications, it is highly desirable to replace mechanical beam-steering components (i.e., mirrors and gimbals) with a nonmechanical device. One such device is a nematic liquid crystal optical phased array (LCOPA). An LCOPA can implement a blazed phase grating to steer the incident light. However, when a phase grating is used in a broadband imaging system, two adverse effects can occur. First, dispersion will cause different incident wavelengths arriving at the same angle to be steered to different output angles, causing chromatic aberrations in the image plane. Second, the device will steer energy not only to the first diffraction order, but to others as well. This multiple-order effect results in multiple copies of the scene appearing in the image plane. We describe a digital image restoration technique designed to overcome these degradations. The proposed postprocessing technique is based on a Wiener deconvolution filter. The technique, however, is applicable only to scenes containing objects with approximately constant reflectivities over the spectral region of interest. Experimental results are presented to demonstrate the effectiveness of this technique.

Diffractive optical elements are finding new and interesting uses in both commercial and military markets, such as holographic scanners, head-up displays, holographic components for optical-disk readout, aberration correction for optical systems, and diffractive elements for monochromatic and broadband imaging systems. In this tutorial the fundamental properties of diffractive optical elements that must be considered in an optical design are emphasized. Methods to incorporate diffractive optical elements into computer-lens-design programs, fabrication techniques, and illustrative applications are also discussed.

Diffractive optical elements (DOEs) remain highly underutilized in broadband optical systems even though different technologies for DOEs including échelette-type gratings (EGs), multilevel DOEs, and metagratings have been introduced. Specifically, nanocomposite-enabled EGs can achieve efficiencies of close to throughout the visible spectrum, but only for relatively small diffraction angles. Therefore, the question remains if they are suitable for high-numerical-aperture (NA) systems. Here we show that this is indeed the case. To this end, we first demonstrate that macroscopic nanocomposite-enabled diffractive lenses (DLs) can achieve perfect broadband focusing up to a NA of 0.03. We then derive analytic relationships and investigate prototypical optical designs to show that this threshold fully covers the requirements of high-end imaging systems with This holistic all-system analysis demonstrates that the individual NA of a DL in a broadband imaging system is one to two orders of magnitude lower than the overall system’s NA. This shows that high-NA flat optical elements are not required for high-NA broadband systems. Therefore, nanocomposite-enabled EGs can unlock the full potential of DOEs for broadband optical systems, whereas other technologies cannot fulfill their high efficiency requirements.

Broadband imaging systems that utilize combinations of holographic lenses can be lightweight and have large apertures. Holographic lenses can be reproduced from a digital master using embossing techniques thus eliminating the high cost of polishing large glass elements. These features are attractive in the visible region and in the infrared where the size of optical elements is limited by available materials. We report a Fresnel-diffraction analysis of a broadband imaging system that consists of three lenses of arbitrary dispersion. A general solution is obtained for the wavelength dependence of the lenses that are required to correct both longitudinal and lateral paraxial chromatic aberration. The solution for the two-lens case is found as an intermediate step and is useful when correction for a single chromatic aberration is desired. From the general solution a specific system configuration is obtained that utilizes holographic elements to produce a well-corrected image in broadband light. An experimental system has been designed using conventional achromats and holographic lenses. Preliminary experiments are reported that demonstrate the performance of this imaging system in both laser and broadband illumination.

The integration of diffractive optical elements (DOEs) into a broadband optical system can often allow for increasing the system’s performance, reducing its size, or its complexity. However, despite considerable efforts to develop different technologies for DOEs, they still remain highly underutilized in broadband imaging system. This is because DOEs that maintain high diffraction efficiencies across the full range of wavelengths, angles of incidence (AOIs), and grating periods required for different optical systems are currently not available. Since the wavelength dependence of the efficiency is fundamentally linked to the dispersion of the phase delay \((\phi (\lambda )\)), this leads to the question of whether the dispersion engineering capabilities of nanocomposites could make such materials an enabling technology for finally unlocking the full potential of DOEs for optical design. In this chapter, I address this question as my first advanced application for nanocomposites. At the same time, my second goal in this chapter is to not restrict myself to one material platform and embodiment of DOEs, but also develop general concepts for how DOEs for broadband systems can be designed.

The delay-and-sum (DAS) beamformer, utilized in current state of the art ultrasound imaging systems, applies time delays on each receive channel to focus the returning echoes and weights the focused RF data on each receive channel prior to beamsummation. Apodization functions like the Hamming and Nuttall windows reduce the sidelobe levels the DAS beamformer's point spread function (PSF). As a result, apodization greatly impacts the contrast and resolution of the final output image. We propose a beamformer architecture for broadband imaging systems that uses unique finite impulse response (FIR) filters on each receive channel The filter weights are constructed to maximize the contrast resolution of the system's spatial response. We present simulation results showing that FIR filters of modest tap lengths (3-7) can yield marked improvement in image contrast and point resolution. This increase in contrast resolution comes at the expense of a decrease in beamformer sensitivity. We investigate the effects of magnitude and phase aberration on the FIR beamformer by simulating near field thin phase screen aberrators. Specifically we examine the performance of the FIR beamformer in the presence of magnitude aberration characterized by an a priori root-mean- square (RMS) strength of 5 dB and a full-width at half-maximum (FWHM) correlation length of 2.1 mm as well as in the presence of phase aberration characterized by an a priori RMS strength of 28 ns and a FWHM correlation length of 3.6 mm. Contrast resolution results show that the aberrated FIR beamformer outperforms the unaberrated DAS beamformer by almost 10 dB. We believe that our array pattern synthesis technique and beamformer architecture have the potential to significantly improve the contrast resolution performance of broadband imaging systems.

Charge-carrier engineering of staggered-gap p-CuAlO2/β-Ga2O3 bipolar heterojunction for self-powered photodetector with exceptional linear dynamic range and stability