Research on the Effect of Vibrational Micro-Displacement of an Astronomical Camera on Detector Imaging.

Scientific-grade cameras are frequently employed in industries such as spectral imaging technology, aircraft, medical detection, and astronomy, and are characterized by high precision, high quality, fast speed, and high sensitivity. Especially in the field of astronomy, obtaining information about faint light often requires long exposure with high-resolution cameras, which means that any external factors can cause the camera to become unstable and result in increased errors in the detection results. This paper aims to investigate the effect of displacement introduced by various vibration factors on the imaging of an astronomical camera during long exposure. The sources of vibration are divided into external vibration and internal vibration. External vibration mainly includes environmental vibration and resonance effects, while internal vibration mainly refers to the vibration caused by the force generated by the refrigeration module inside the camera during the working process of the camera. The cooling module is divided into water-cooled and air-cooled modes. Through the displacement and vibration experiments conducted on the camera, it is proven that the air-cooled mode will cause the camera to produce greater displacement changes relative to the water-cooled mode, leading to blurring of the imaging results and lowering the accuracy of astronomical detection. This paper compares the effects of displacement produced by two methods, fan cooling and water-circulation cooling, and proposes improvements to minimize the displacement variations in the camera and improve the imaging quality. This study provides a reference basis for the design of astronomical detection instruments and for determining the vibration source of cameras, which helps to promote the further development of astronomical detection.

Extreme learning machine and genetic algorithm in quantitative analysis of sulfur hexafluoride by infrared spectroscopy: erratum.

This erratum reports corrections for the original publication, Appl. Opt.61, 2834 (2022)APOPAI0003-693510.1364/AO.450805.

Non-defocus high transmittance image slicer.

The first non-defocus high transmittance non-fiber image slicer is presented. In order to solve the problem of image blur caused by the defocus between different sliced sub-images, an optical path compensation method based on stepped prism plate is proposed. Design results show that both the maximal defocus amount between the four sliced sub-images is reduced from 2.363 mm to nearly 0. The diameter of the dispersion spot on the focal plane is reduced from 98.47 µm to close to 0. The optical transmittance of the image slicer is up to 91.89%. This new image slicer is greatly valuable for high resolution and high transmittance spectrometer.

Quantum Dot-Based Micromotors with NIR-I Light Photocatalytic Propulsion and NIR-II Fluorescence.

Here, we report the first PbS quantum dot (QD)-based micromotors with NIR-I light-driven photocatalytic propulsion and NIR-II fluorescence. Under the irradiation of NIR-I light (808 nm), PbS QD-doped cuprous oxide (Cu2O@PbS) micromotors can display efficient propulsion in a variety of biocompatible fuels such as malic acid, glucose, and urea. Among them, the Cu2O@PbS micromotors exhibit the best propulsion performance in a very low concentration of malic acid, with an average speed as high as 11.86 µm/s. The enhanced NIR-I photocatalytic activity of Cu2O@PbS micromotors benefits from the doping of NIR-I PbS QDs that can be excited by NIR-I light and exhibit high electron transport efficiency. The doped PbS QDs can effectively increase the absorption efficiency of the micromotors in the NIR-I region while also inhibiting the recombination of photogenerated electron-hole pairs. Interestingly, due to the presence of NIR PbS QDs, the Cu2O@PbS micromotors demonstrate prominent and stable NIR-II fluorescence (emission wavelength: 1100 nm), which offer promising potential for visualization of their position in vivo. In comparison to other photocatalytic micromotors, the simple fabrication strategy, excellent NIR-II fluorescence, together with the NIR-I light-dependent propulsion behavior of the current Cu2O@PbS micromotors, thus pave the way for further development of advanced smart "robots" for intelligent biomedical applications.

Extreme learning machine and genetic algorithm in quantitative analysis of sulfur hexafluoride by infrared spectroscopy.

Owing to the general disadvantages of traditional neural networks in gas concentration inversion, such as slow training speed, sensitive learning rate selection, unstable solutions, weak generalization ability, and an ability to easily fall into local minimum points, the extreme learning machine (ELM) was applied to sulfur hexafluoride (SF6) concentration inversion research. To solve the problems of high dimensionality, collinearity, and noise of the spectral data input to the ELM network, a genetic algorithm was used to obtain fewer but critical spectral data. This was used as an input variable to achieve a genetic algorithm joint extreme learning machine (GA-ELM) whose performance was compared with the genetic algorithm joint backpropagation (GA-BP) neural network algorithm to verify its effectiveness. The experiment used 60 groups of SF6 gas samples with different concentrations, made via a self-developed Fourier transform infrared spectroscopy instrument. The SF6 gas samples were placed in an open optical path to obtain infrared interference signals, and then spectral restoration was performed. Fifty groups were randomly selected as training samples, and 10 groups were used as test samples. The BP neural network and ELM algorithms were used to invert the SF6 gas concentration of the mixed absorbance spectrum, and the results of the two algorithms were compared. The sample mean square error decreased from 248.6917 to 63.0359; the coefficient of determination increased from 0.9941 to 0.9984; and the single running time decreased from 0.0773 to 0.0042 s. Comparing the optimized GA-ELM algorithm with traditional algorithms such as ELM and partial least squares, the GA-ELM algorithm had higher prediction accuracy and operating efficiency and better stability and generalization performance in the quantitative analysis of small samples of gas under complex noise backgrounds.

Cross-domain heterogeneous residual network for single image super-resolution.

Single image super-resolution is an ill-posed problem, whose purpose is to acquire a high-resolution image from its degraded observation. Existing deep learning-based methods are compromised on their performance and speed due to the heavy design (i.e., huge model size) of networks. In this paper, we propose a novel high-performance cross-domain heterogeneous residual network for super-resolved image reconstruction. Our network models heterogeneous residuals between different feature layers by hierarchical residual learning. In outer residual learning, dual-domain enhancement modules extract the frequency-domain information to reinforce the space-domain features of network mapping. In middle residual learning, wide-activated residual-in-residual dense blocks are constructed by concatenating the outputs from previous blocks as the inputs into all subsequent blocks for better parameter efficacy. In inner residual learning, wide-activated residual attention blocks are introduced to capture direction- and location-aware feature maps. The proposed method was evaluated on four benchmark datasets, indicating that it can construct the high-quality super-resolved images and achieve the state-of-the-art performance. Code and pre-trained models are available at https://github.com/zhangyongqin/HRN.

Design and characterization of a thermally stabilized fiber Fabry-Perot etalon as a wavelength calibrator for high-precision spectroscopy.

Filtering light from a broadband source with a Fabry-Perot etalon generates comb-like peaks in the spectral domain that can serve as calibration reference for precise Doppler shift detection on astronomical spectrographs. Fiber Fabry-Perot etalons are small in size and easily aligned optically. In application, high thermal sensitivity of the fiber core material requires a highly stable temperature control system. Here, we report on the design, characterization, and thermal performance of a fiber Fabry-Perot etalon-based calibrator system insensitive to environmental temperature perturbation, aimed as a reference for m⋅s-1 precision radial velocity measurements. A fast and simple method to estimate the etalon finesse and a dual-loop approach to achieve sub-millikelvin temperature fluctuation are proposed and demonstrated.

Optimal optical path difference of an asymmetric common-path coherent-dispersion spectrometer.

Optical path difference (OPD) is a very significant parameter in the asymmetric common-path coherent-dispersion spectrometer (CODES), which directly determines the performance of the CODES. In order to improve the performance of the instrument as much as possible, a temperature-compensated optimal optical path difference (TOOPD) method is proposed. The method does not only consider the influence of temperature change on the OPD but also effectively solves the problem that the optimal OPD cannot be obtained simultaneously at different wavelengths. Taking the spectral line with a Gaussian-type power spectral density distribution as a representative, the relational expression between the OPD and the visibility of interference fringes formed by the CODES is derived for the stellar absorption/emission line. Further, the optimal OPD is deduced according to the efficiency function, and the relationship between the optimal OPD and wavelength is analyzed. Then, based on the materials' dispersion characteristics, different optical materials are combined and added to the interferometer's reflected and transmitted optical path to implement the optimal OPD at different wavelengths, thereby improving the detection precision. Meanwhile, the materials whose refractive index negatively changes with temperature are selected to reduce or even offset the temperature impact on OPD, and hence the system's stability is improved and further improves the detection precision. Under certain input conditions, the material combination that approximates the optimal OPD is performed within the range of 0.66-0.9 µm. The simulation results show that the maximal difference between the optimal OPD obtained by the efficiency function and the OPD produced by the material combination is 0.733 mm for the absorption line and 1.122 mm for the emission line, which is reduced by 1 time compared with only one material. The influence of temperature on the OPD can be reduced by 2-3 orders of magnitude by material combination, which greatly ameliorates the stability of the whole spectrometer. Hence, the TOOPD method provides a new idea for further improving the high-precision radial velocity detection of the asymmetric common-path CODES.

W-shaped common-path interferometer.

We present a novel static W-shaped common-path interferometer. In particular, the W-shaped common-path corner-cube retroreflector interferometer (W-CPRI) is introduced via detailed analysis of its working principles and performance. It comprises two corner-cube retroreflectors (CCRs), a reflecting mirror (RM), and a beam splitter. For each interference output of an ideal W-CPRI, the two beams recombine and have the same output direction, including a tilted CCR. In a deformed W-CPRI structure, an optical path difference can be produced by inserting an optical element that changes the optical path in the interferometer arm of the W-CPRI. The posture deviations of the RM and the CCRs in the W-CPRI are analyzed. In addition, a proof-of-concept experiment is conducted, with the stability analyzed using the fringe similarity method. The average cosine similarity is 0.9953, revealing that this W-CPRI has high stability and strong coherence while avoiding the tilt and displacement of the interferometer arm.

A Review of Functional Near-Infrared Spectroscopy Studies of Motor and Cognitive Function in Preterm Infants.

Preterm infants are vulnerable to brain injuries, and have a greater chance of experiencing neurodevelopmental disorders throughout development. Early screening for motor and cognitive functions is critical to assessing the developmental trajectory in preterm infants, especially those who may have motor or cognitive deficits. The brain imaging technology functional near-infrared spectroscopy (fNIRS) is a portable and low-cost method of assessing cerebral hemodynamics, making it suitable for large-scale use even in remote and underdeveloped areas. In this article, we review peer-reviewed, scientific fNIRS studies of motor performance, speech perception, and facial recognition in preterm infants. fNIRS provides a link between hemodynamic activity and the development of brain functions in preterm infants. Research using fNIRS has shown different patterns of hemoglobin change during some behavioral tasks in early infancy. fNIRS helps to promote our understanding of the developmental mechanisms of brain function in preterm infants when performing motor or cognitive tasks in a less-restricted environment.

[Measurements of the concentration of atmospheric CO2 based on OP/FTIR method and infrared reflecting scanning Fourier transform spectrometry].

The present paper describes the observations and measurements of the infrared absorption spectra of CO2 on the Earth's surface with OP/FTIR method by employing a mid-infrared reflecting scanning Fourier transform spectrometry, which are the first results produced by the first prototype in China developed by the team of authors. This reflecting scanning Fourier transform spectrometry works in the spectral range 2 100-3 150 cm(-1) with a spectral resolution of 2 cm(-1). Method to measure the atmospheric molecules was described and mathematical proof and quantitative algorithms to retrieve molecular concentration were established. The related models were performed both by a direct method based on the Beer-Lambert Law and by a simulating-fitting method based on HITRAN database and the instrument functions. Concentrations of CO2 were retrieved by the two models. The results of observation and modeling analyses indicate that the concentrations have a distribution of 300-370 ppm, and show tendency that going with the variation of the environment they first decrease slowly and then increase rapidly during the observation period, and reached low points in the afternoon and during the sunset. The concentrations with measuring times retrieved by the direct method and by the simulating-fitting method agree with each other very well, with the correlation of all the data is up to 99.79%, and the relative error is no more than 2.00%. The precision for retrieving is relatively high. The results of this paper demonstrate that, in the field of detecting atmospheric compositions, OP/FTIR method performed by the Infrared reflecting scanning Fourier transform spectrometry is a feasible and effective technical approach, and either the direct method or the simulating-fitting method is capable of retrieving concentrations with high precision.

[Design and implementation of real-time processing platform for movement error correction of hyperspectrual imaging].

The approach that deals with compressed and packed image data transmitted from satellite to the ground is too slow for real-time application occasion, it also has huge image, multi-processing step and complexity recovery arithmetic synchronously, so it is urgent to build accurate and fast data processing platform for real-time processing. For the moment, the platform for data recovery and error correction is much less, the so-called successful platform may directly affect the effect of target detection and identification because of processing speed, precision, flexibility, configuration and upgrade. The platform we build is to set spatial modulation spectrometer as the research goal, We design and implement a hardware platform based on Xilinx Virtex-5 FPGA, It is combined with ISE IP soft-core resources which is configurable, high-precision and flexible by focusing on analyzing key aspects of the hardware platform. And the relevant test data were drawn, then a good way for spectrum recovery and error correction was explored.

[The melioration on spectra response heterogeneity of hadamard transform spectral imager].

Hadamard transform optics has been developed in the past decades. It has been used in distinguishing targets, detecting feeble signals and so on. Hadamard transform spectral imager (HTSI), based on digital micro-mirror device, is a new dispersion spectral imager. HTSI has been developed in our laboratory. The spectral heterogeneity of encoded image captured by HTSI has been researched according to spectrum calibration in this paper. Relative and absolute spectrum emittance calibration algorithms have been proposed first time on HTSI to meliorate the spectrum heterogeneity. It aims at the problem that the accuracy of recovered spectrum is depressed by the heterogeneity noise and disorder encoding spectrum in spectral image. Simulation and experiment result have demonstrated that the meliorated spectral curve is close to the standard spectrum, and the variance of the recovered spectrum ranges from 2.4% to 4.2% with regard to the spectral image of 7 waves. This is fully satisfied for the requirement of laboratory and projects.

[Research on endmember extraction algorithm based on spectral classification].

Spectral unmixing is an important task for data processing of hyperspectral remote sensing, which is comprised of extracting the pure spectra (endmember) and calculating the abundance value of pure spectra. The most efficient endmember extracting algorithms (EEAs) is designed based on convexity geometry such as pure pixel index (PPI), N-finder algorithm (N-FINDR). Most EEAs choose pure spectra from all pixels of an image so that they have disadvantages like slow processing speed and poor precision. Partial algorithms need reducing the spectral dimension, which results in the difficulty in small target identification. This paper proposed an algorithm that classifies the hyperspetral image into some classes with homogeneous spectra and considers the mean spectra of a class as standard spectra for the class, then extracts pure spectrum from all standard spectra of classes. It reduces computation and the effect of system error, enhancing the speed and precision of endmember extraction. Using the least squares with constraints on spectral extraction and spectral unmixing, by controlling the band average value of the maximum spectral redundant allowance to control the number of endmembers, does not need to reduce the spectral dimension and predetermine the number of endmembers, so compared to N-finder algorithm, such algorithm is more rational.

Designs of multipass optical configurations based on the use of a cube corner retroreflector in the interferometer.

We describe designs of the multipass optical configurations of an interferometer with high spectral resolution with respect to 6, 12, and 24 times more optical passes than the conventional Michelson interferometer. In each design, a movable cube corner retroreflector is combined with a folding reflector group (FRG) as the interferometer's moving combination to implement the multipass optical configuration with the characteristic of surface division. Analyses reveal that when there are 12 or more optical passes, the net effect of the ray's angular deviation of the entire moving combination amounts to only the alignment error of one of the reflectors in the FRG, demonstrating the self-aligning property of the interferometer.

[General expression of optic path difference of reflecting rotating Fourier transform spectrometer].

The principle of reflecting rotating Fourier transform spectrometer was introduced in the present paper. Based on the Malus law and reflecting characteristic of cube corner, the optic path difference of reflecting rotating Fourier transform spectrometer was analyzed and calculated by choosing the center of rotating mirror as a reference point of the aplanatic surface of incidence beam and return beam. General expression of optic path difference at any time and maximal optic path difference of reflecting rotating Fourier transform spectrometer was presented. The factors that influence the maximal optic path difference and the period of optic path difference were analyzed. The results provide a theoretical guidance for design and manufacture of reflecting rotating Fourier transform spectrometer.

[Research on spectral classification algorithm based on spatial feature].

With the wide use of imaging spectroscopy, applying data cubes to classification and identification of materials has been developed to be an important research content. The classification algorithms play a vital role in accuracy and precision of object identification. The most common classification algorithms mainly make use of the information gained from spectral dimension and classify the materials based on spectral match. The material reflectance spectra collected by imaging spectroscopy is determined not only by the sorts, but also by the geometry structure and roughness of material surface, and so on. Then classification and identification algorithms only using the reflection spectra have errors to some extent. This paper puts forward an algorithm based on the common classification algorithms that controls the classification process by using the spatial feature of image to promote the correctness of classification. This algorithm was applied to identify the true leaves from the fake ones. The result shows preferable spatial continuity. To a great extent, the algorithm overcomes "ma pixel" domino effect, and is proved valid.

[Developments and trends of the computed tomography imaging spectrometers].

The present paper reviews the computed tomography imaging spectrometer (CTIS) measurement systems at home and abroad from the aspects of technological characterizations and research focuses. The developments of computed tomography imaging spectrometers are described, involving the adding new abilities by improving systematic structure and by incorporating other elements or systems, the study and applications of novel grating elements, detectors or apparatus, the optimizations and improvements of the system calibration methods and reconstruction algorithms. In addition, based on the classification of application scope, the extension status of probing spectral bands and application fields towards computed tomography imaging spectrometers and related systems are summarized. The principles of non-scanning computed tomography imaging spectrometer and high-throughput computed tomography imaging spectrometer are introduced. Moreover, the trends of computed tomography imaging spectrometers are discussed too.

[Comparison of correction methods for nonlinear optic path difference of reflecting rotating Fourier transform spectrometer].

The principle of reflecting rotating Fourier transform spectrometer was introduced in the present paper. The nonlinear problem of optical path difference (OPD) of rotating Fourier transform spectrometer universally exists, produced by the rotation of rotating mirror. The nonlinear OPD will lead to fictitious recovery spectrum, so it is necessary to compensate the nonlinear OPD. Three methods of correction for the nonlinear OPD were described and compared in this paper, namely NUFFT method, OPD replace method and interferograms fitting method. The result indicates that NUFFT was the best method for the compensation of nonlinear OPD, OPD replace method was better, its precision was almost the same as NUFFT method, and their relative error are superior to 0.13%, but the computation efficiency of OPD replace method is slower than NUFFT method, while the precision and computation efficiency of interferograms fitting method are not so satisfied, because the interferograms are rapid fluctuant especially around the zero optical path difference, so it is unsuitable for polynomial fitting, and because this method needs piecewise fitting, its computation efficiency is the slowest, thus the NUFFT method is the most suited method for the nonlinear OPD compensation of reflecting rotating Fourier transform spectrometer.

[Spatially modulated interference Hadamard transform spectral imager].

The principle and instrumental structure of dispersion Hadamard transform spectral imager were briefly described in the present paper, and the disadvantages of the imager both in dislocation of spatial and spectral information and in spectral resolution limited by the width of Hadamard encoding mask were pointed out. A new instrumental principle and design of spatially modulated interference Hadamard transform spectral imager was proposed. A lateral shearing interferometer was used to acquire interference signals of all the Hadamard encoding information at different optical path difference. Then the methods of Fourier transform and Hadamard transform for interferogram were performed to acquire the spectra of objectives. Theory analysis of this imager demonstrated that the modulation of interferogram would not be affected by some factors such as the form and size of Hadamard encoding mask, and the spectral resolution would not be influenced by the size of Hadamard encoding mask. Furthermore, such technique not only effectively eradicated the dislocation of spatial information and spectral information existing in dispersion Hadamard transform spectral imager, but also made it convenient to image with high-throughput, high spatial resolution and high spectral resolution.