Anthropogenic emissions of greenhouse gases (GHGs), particularly carbon dioxide (CO2) and methane (CH4), constitute the primary drivers of global warming. Controlling anthropogenic emissions is crucial in mitigating global warming. Satellite remote sensing technology is considered the most viable and effective technological support for carbon monitoring. Global-scale, long-term carbon monitoring enhances understanding of human activities' impact on carbon cycles and climate change, while high spatiotemporal resolution carbon monitoring in key regions aims to provide data support in reducing anthropogenic emissions. Passive optical remote sensing is considered the primary technological means for satellite-based carbon monitoring. The satellite-borne passive remote sensing detection technologies successfully validated in orbit include Michelson interferometric spectroscopy, grating spectroscopy, Fabry-Pérot technology, and spatial heterodyne interferometric spectroscopy. This article reviews recent advancements in optical solutions for remote sensing payloads. It thoroughly analyzes the optical performance metrics of these payloads, comparing the strengths and weaknesses of different detection technologies through optical scheme analyses. Furthermore, specific metrics and development trends for passive payloads used in high spatiotemporal resolution remote sensing of key areas have been discussed. Finally, considering the technical requirements for China's next-generation carbon satellite. A novel static interferometric imaging technique is proposed, which combines spatial heterodyne interferometric spectral technology with azimuthal arc vector orthogonal direction heterogeneous optical field modulation. This innovative technology retains the advantages of traditional spatial heterodyne interferometry with high optical throughput and spectral resolution, while introducing new modulation techniques for enhanced spatial resolution. It is anticipated to advance global environmental protection and mitigating climate change.
Raman spectroscopy has emerged as an essential technique for material composition analysis due to its noncontact, nondestructive, and rapid characteristics. Spatial heterodyne spectroscopy offers the advantages of high stability, high throughput, and ultra-high spectral resolution, making it particularly suitable for Raman spectroscopic detection. The main design parameters of a spatial heterodyne Raman detection system were determined under near-infrared wavelength excitation: a Raman shift detection range of 300 to 2000 cm−1 and a spectral resolution of 5 cm−1 at an excitation wavelength of 785 nm. The optical design of the dispersion module and imaging module was completed. Test results demonstrate that the spectrometer achieves a spectral resolution of 5.33 cm−1 and can detect Raman shifts in the range of 315 to 2131.6 cm−1. Verification tests on cyclohexane and lipstick samples confirm that the system exhibits excellent fluorescence suppression capability, with a signal-to-noise ratio of the cyclohexane Raman peak reaching 1600.8.
In order to improve the real-time performance of the division-of-time polarization imaging system applied in dynamic scenes, the traditional rotating polarizer imaging scheme is improved and a fast-rotating polarization imaging system is designed. The scheme of the camera exposing during the uniform rotating of the polarizer is applied in the system, and the intensity images of different polarization angles are collected when a designed hollow turntable drive the polarizer to rotate rapidly. Based on the brief introduction of the principle of the polarization imaging system of fast rotating polarizer, the optical-mechanical structure design and core components of the system are introduced in detail, and the polarization imaging experiment of the system is carried out. The pipeline calculation method and the least square method are used to solve 5 adjacent intensity images of the target scene every time to calculate the degree of linear polarization (DoLP) and the angle of polarization (AoP). The test results show that the system can get polarization images at a frame rate of 80 frames per second (FPS) or with the pixels of 1280×1180. It is shown that when the imaging frame rate is 51 FPS, the polarization images obtained by solving 5 consecutive frames of intensity images have better detail recognition ability than those obtained by solving 3 consecutive frames of intensity images. Compared with the division-of-time polarization imaging system of the start-stop rotating polarizer, this division-of-time polarization imaging system with fast rotating polarizer increases the polarization imaging frame rate, improves the real-time performance, and enhances the detection ability to dynamic scenes.
The temperature structure of the global mesosphere and lower atmosphere (MLT) is significant for the study of atmospheric physical, chemical and kinetic processes. Oxygen (O2) A-band airglow (762 nm) can be used as an important tracer to detect the atmospheric temperature structure. The advantage of spatial heterodyne spectrometer (SHS) is high stability, high throughput and high spectral resolution. The fine spectral structure of A-band night glow is detected by limb observation combined with simultaneous split field imaging of atmospheric vertical profile, and the temperature information is retrieved by recovering spectra. Building an accurate forward model is the premise and foundation to obtain the global spaceborne high-resolution atmospheric temperature structure. Based on the A-band night glow radiation mechanism, molecular spectroscopy theory, atmospheric radiation transfer theory and the detection principle of SHS, this paper constructs the forward model of target airglow observation. Furthermore, the sensitivity and analysis of the influencing parameters of the forward model is carried out, which provides a theoretical basis fort the forward modes modification and instrument design. The results show that the forward model described in the paper can satisfy the simulation of A-band night glow spectral radiance observed by SHS at any location through limb observation combined with simultaneous split field of atmospheric vertical profile. That is, the atmospheric tangent range covers 80-120 km and the vertical resolution is better than 2 km. It lays a foundation for the space-borne SHS to detect and accurately retrieve the global temperature structure in MLT region.
As semiconductors' critical dimension decreases, higher precision inspection instruments are needed to detect defects in the manufacturing process. Optical inspection methods based on light and dark field microscopy can detect defects on large wafer areas well without damaging the wafer, but the minimum detectable defect size is limited because the defect scattering signal is easily buried by the scattering background noise from the wafer's rough surface. To detect submicron defects on wafer surfaces, a spot-scanning laser scattering scheme is developed based on the dark-field scattering technique. Using the Finite Difference Time Domain (FDTD) method and the inspection scheme, an electromagnetic scattering model of the defect on the wafer surface is established, and the defect characteristics and electromagnetic field distribution are simulated. Moreover, the effects of the collecting aperture angle on the signal intensity of defects and the discrimination of defects of different sizes, as well as the effects of the incident angle on the scattered signal intensity of submicron defects, are examined. A spot-scanning laser scattering experimental platform was built, and 200 nm, 1 μm, and 5 μm diameter polystyrene latex (PSL) spheres were deposited on the wafer surface to verify the validity of the proposed method. Signals of the three sizes of spheres were detected in the stitched images with good discrimination of signal intensity, and the signal of the 200 nm PSL sphere displayed a peak signal-to-noise ratio of 32.07 dB. This method provides a reference for further industrialized defect detection systems on wafer surfaces.
In order to achieve high sensitivity, accuracy and fast measurement of ellipsometry system, a phase modulation ellipsometry system based on Photoelastic Modulator (PEM) is adopted. At present, the phase delay of the Photoelastic Modulator is generally obtained by using the digital Lock-in Amplifier to extract the harmonic component and the DC component. The high frequency signal is discarded and the static phase delay of the Photoelastic Modulator is set as constant in the calculation process using the digital Lock-in Amplifier. However, the fluctuation of system parameters such as temperature, incident Angle and input signal will cause the decrease of measurement accuracy. In order to avoid the measurement error caused by traditional methods, an optimization method is proposed to calibrate the ellipsometry system with phase modulation. The nonlinear least square method is used to transform the ellipsometry measurement system into an optimization model, and the best match between the estimated value and the observed value is found. In order to verify the proposed optimization calibration method, the digital Lock-in Amplifier and the optimization method were used to scale the measurement system respectively, and the phase delay under the two methods were obtained respectively. The calculated deviations of the calibration of the two methods were 0.1805 and 0.141rad respectively, and the fluctuation of 1h calibration results was less than 1%. The results show that this method can reduce the influence of system parameter error on the measurement accuracy.
KEYWORDS: Signal to noise ratio, Semiconducting wafers, Image segmentation, Signal detection, Inspection, Defect inspection, Signal processing, Image processing, Defect detection
The reagent residue on the unpolished wafer surface will hinder the performance of semiconductor materials. Due to the limited sensitivity and dynamic range of conventional optical detection systems, the residue defects are difficult to detect. A multi-channel spot scanning defect inspection system (SSDIS) is applied to detect the macro reagent residue defects on unpolished wafer. The experiment illustrates that the reflective channel detector is more sensitive to the reagent residue defect. Because of surface roughness of unpolished wafers, the macro reflected defect signal detected by SSDIS always has a low signal-to-noise ratio (SNR) and is hard to analyze. A simple and effective residue defect detection method based on discrete cosine transform (DCT) with OTSU is proposed and implemented. The experimental results showed that the reagent residue with low SNR can be detected accurately.
Aiming at the spaceborne detection application of mid-wave infrared interference imaging spectrometer, a temporally and spatially modulated interference imaging spectrometer detection scheme based on spatial heterodyne spectroscopy is presented. With the motion of the satellite platform or push-sweep mechanism, the interference modulation signals of different optical path in the same spatial resolution unit are obtained in time-sharing. After interference data reconstruction and spectral restoration, the spectral signals in each spatial resolution unit are finally obtained. The spectrometer consists of a pre-collimating objective unit, a static interferometer unit, an imaging unit and a focal plane unit, which can obtain three-dimensional data cubes of images and spectra at the same time. The spectrometer has the characteristics of large luminous flux, stable structure, miniaturization and so on. Under the requirement that the mid-wave infrared band is 3.7~4.8μm and the spectral resolution is better than that of 3cm-1, taking the characteristic spectrum detection of spaceborne mid-wave infrared typical targets is carried out with F#4 focal plane module as an example, the design process and results of the optical system are given. The results show that the design of the optical system meets the requirements of the detection index, which lays a foundation for the remote sensing application of spaceborne high-resolution mid-wave infrared interference imaging spectroscopy.
Spatial heterodyne spectroscopy has the characteristics of hyperspectral resolution, no moving parts and high light flux. It can be used in many fields such as atmospheric composition and physical parameters measurement, astronomical observation and Raman spectrum detection. The limited number of detector pixels in traditional spatial heterodyne spectrometer can only measure a small range near the selected frequency of Littrow wavenumber, while the echelle gratings were used instead of the diffraction gratings, and the grating were rotated at an appropriate angle to separate the spatial dimension of the interferogram of the plane array, i.e. two-dimensional spatial heterodyne spectroscopy. On the premise of not reducing spectral resolution, the detection spectral range was greatly broadened. The spectral calibration method was studied for the experimental device of two-dimensional spatial heterodyne spectrometer. Firstly, the processing flow from the measured interferogram to the restored spectrum was given, and the flat field, apodization and zero filling methods of two-dimensional data were mainly introduced. According to the principle of two-dimensional interference, single- order spectral resolution, effective spectral range and multi-order calibration method are determined. Spectral calibration verification experiments were carried out on the experimental device by using Hg hollow cathode lamp in the laboratory, and the results of spectral calibration were given.
OH radicals in the upper and middle atmosphere are important oxidants and play an important role in atmospheric photochemistry. Current space-based payload can only obtain profile information. In view of the inhomogeneity of atmospheric two-dimensional distribution field, a hyper-spectral OH radical tomography detection scheme based on one-dimensional imaging spatial heterodyne spectroscopy is proposed. In this paper, the basic principle of SHS is introduced. Then it introduces the detection mode of computer chromatography and the principle of atmospheric inversion. Finally, it introduces the design of OH chromatography sounder based on the principle of SHS technology. In order to verify the effectiveness of the design, the data simulation is carried out.
The addition of potassium salt to the propellant of aircraft can effectively reduce the secondary combustion of the wake flame and the difference between the background radiation, which makes the targets detection more difficult for traditional infrared method. Based on high-spatial-resolution, high-throughput and compact spatial heterodyne spectroscopy(SHS), the dynamic target monitoring spectrometer(DTS)detects the potassium spectral lines of 766.49 nm and 769.90 nm by combining the one-dimensional spatial imaging with the two-dimensional orthogonal detection mode. The spectral range and resolution of the two channels of DTS were calibrated by the hyperspectral monochromatic uniform light source scanning system. The relative response consistency correction and absolute response coefficients of the two channels were calibrated by using the large-aperture integrating sphere, and the target spectral lines were extracted by background difference and target spectral line isolation. The target spatial was located and spectrum synthesis was carried out according to the spectral and radiation calibration results and the corresponding relation of the two-dimensional field of view. Finally, a complete data processing flow of DTS is established. In order to test the DTS developed by the laboratory, the target was simulated by adding K2SO4 to the burning alcohol in the outdoor environment. The detected target was successfully recorded through two-channel spectrum synthesis, showing the dynamic change process under the influence of outdoor wind during the combustion process, which verified the rationality of the processing flow.
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