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This work presents an overview of the in-flight engineering data of the Energetic Particle Detector (EPD) instrument suite during its first year of operation. EPD is part of the in-situ scientific payload of the ESA/NASA Solar Orbiter mission which was launched in February 2020. After completion of its commissioning phase, Solar Orbiter started its cruise phase in June 2020, in coincidence with its first perihelion at 0.51 au. Six remote-sensing instruments and four in-situ instruments, including EPD, which is a suite of four individual sensors, make Solar Orbiter the most complete space laboratory flown into the inner heliosphere to date. In-flight engineering data of the different EPD units such as their power consumption and their temperatures are the key indicators to ascertain that the design, manufacturing and qualification of the EPD units on ground and throughout the different life cycles prior to launch were successful. On the other hand, these in-flight housekeeping data also reflect the general status of the units which are exposed to space radiation, stray light and a varying thermal environment. The reliability of the EPD suite was analyzed during the design phase and the in-flight status evaluation confirms this analysis. The first year of flight covers special milestones for the Solar Orbiter mission such as the launch, first perihelion, as well as the first Venus flyby. By evaluating the in-flight engineering data, it is demonstrated that the EPD suite successfully meets its design requirements and also satisfies its scientific objectives in flight.

The phase induced intensity noise (PIIN) may seriously reduce the signal-to-noise ratio (SNR) of continuous-wave coherent Doppler lidar (CW-CDL), thereby limiting its performance in practical applications. In this paper, we propose to use optical frequency domain reflectometry (OFDR) technique to locate the PIIN sources and evaluate their intensities. According to the OFDR information, we demonstrate that the PIIN in our CW-CDL system is mainly induced by the crosstalk of polarization beam splitter. Then, the PIIN is reduced by setting fiber delay line, polarization control, and AR-coating. Finally, a wind Doppler signal at a distance of 80 meters is obtained on a clear day, and a typical SNR of 19.4 dB is achieved.

MethaneAIR is the airborne simulator of MethaneSAT, an area-mapping satellite currently under development with the goal of locating and quantifying large anthropogenic CH4 point sources as well as diffuse emissions at the spatial scale of an oil and gas basin. Built to closely replicate the forthcoming satellite, MethaneAIR consists of two imaging spectrometers. One detects CH4 and CO2 absorption around 1.65 and 1.61 µm, respectively, while the other constrains the optical path in the atmosphere by detecting O2 absorption near 1.27 µm. The high spectral resolution and stringent retrieval accuracy requirements of greenhouse gas remote sensing in this spectral range necessitate a reliable spectral calibration. To this end, on-ground laboratory measurements were used to derive the spectral calibration of MethaneAIR, serving as a pathfinder for the future calibration of MethaneSAT. Stray light was characterized and corrected for through fast-Fourier-transform-based Van Cittert deconvolution. Wavelength registration was examined and found to be best described by a linear relationship for both bands with a precision of ∼ 0.02 spectral pixel. The instrument spectral spread function (ISSF), measured with fine wavelength steps of 0.005 nm near a series of central wavelengths across each band, was oversampled to construct the instrument spectral response function (ISRF) at each central wavelength and spatial pixel. The ISRFs were smoothed with a Savitzky–Golay filter for use in a lookup table in the retrieval algorithm. The MethaneAIR spectral calibration was evaluated through application to radiance spectra from an instrument flight over the Colorado Front Range.

Waveguide technology has great prospects of development in optical see-through near-eye displays with larger field of view, lower thickness and lighter weight than other conventional optical technologies. However, the stray light is usually inevitable in current optical design and manufacturing, causing a poor imaging quality. In this paper, the principle and structures of stray light generation are analyzed, and the causes are discussed by non-sequential ray-tracing with mass precision calculation. From the ray-tracing, the suppression of stray light by optimizing design and manufacturing are achieved. A 2 mm-thickness geometrical waveguide with partially reflective mirror array is designed. The field of view of the optimized geometrical waveguide reaches 47° with 10 mm at exit pupil diameter and 20 mm at eye relief.

Previously, a telepresence system, called Levitar, was proposed to allow communication through computer-graphics (CG) avatars in real space. Levitar employs micro-mirror array plates (MMAPs) to display mid-air images and optically transfer the camera viewpoint to the mid-air image-display position optically. This system captures the first-person view of a mid-air image avatar; however, it has a limitation that the stray light caused by MMAPs reduces its range. Therefore, in this study, we propose an optical system to capture a wider range of mid-air viewpoints. The proposed optical system uses aerial imaging by retro-reflection (AIRR) instead of MMAPs for mid-air image display and camera viewpoint transfer. AIRR is a mid-air imaging system that includes a beam splitter and retro-reflector. However, in contrast to MMAPs, it does not generate stray light. The optical transfer of the camera viewpoint by AIRR enables the capture of a large area. To evaluate the range of the capturing area when using cameras with MMAPs and AIRR, we conducted experiments under different camera gaze directions and effective angle of view. The results indicate that AIRR maintains a constant resolution up to 40° of the camera gaze direction, whereas MMAPs have a lower resolution above 30°, and the area of the marker detection rate of over 80% is approximately 54% larger for AIRR than for MMAPs. This implies that AIRR achieved a wider imaging range than MMAPs for mid-air telepresence systems.

Modern small-sized spectrometers are mainly designed by the Czerny–Turner scheme with a flat diffraction grating or, if the goal is to obtain the maximum aperture at the expense of resolution, by the scheme with a concave diffraction grating. In such spectrometers, the spectrum is registered by photodiode array. In this work, we provide an overview of characteristics of the compact spectrometers developed by our group. These spectrometers use caseless linear photodiode arrays for spectrum registration that eliminates the reflection of radiation from the cover glass of the photodiode array and reduces stray light. The tightness of the housing of spectrometers prolongs their service life. The parameters of the spectrometer modifications designed according to the Czerny–Turner scheme are given. The main advantage of the spectrometer of this type is the low stray light inside the device and the same spectral resolution throughout the spectral range. Aberrations limit the working aperture in the Czerny–Turner scheme to 1/6. The scheme with a flat field allows operation with a larger working aperture. Three modifications of the spectrometer have been developed according to this scheme; a description of their main parameters is given. The results of experimental comparison of the light gathering power and spectral resolution of spectrometers with different optical schemes, as well as the examples of their application, are presented. Devices designed according to the Czerny–Turner scheme are used in atomic emission and atomic absorption spectral analysis and in spectrophotometry for registration of absorption spectra of condensed media. The spectrometers with flat field are used for recording luminescence and Raman spectra of minerals. The developed compact spectrometers can work in a spectral range of 190–1100 nm with the width of the recorded spectral range from 70 to 1000 nm; the best spectral resolution is 0.1 nm, the stray light level is less than 0.05%, and the maximum measured optical density exceeds 3. Owing to a large working aperture of 1 : 2.1, the flat field spectrometers have an increased light gathering power.

We introduce a new approach to reduce uncorrelated background signals from fluorescence imaging data, using real-time subtraction of background light. This approach takes advantage of the short fluorescence lifetime of most popular fluorescent activity reporters, and the low duty-cycle of ultrafast lasers. By synchronizing excitation and recording, laser-induced multiphoton fluorescence can be discriminated from background light levels with each laser pulse. We demonstrate the ability of our method to – in real-time – remove image artifacts that in a conventional imaging setup lead to clipping of the signal. In other words, our method enables imaging under conditions that in a conventional setup would yield corrupted data from which no accurate information can be extracted. This is advantageous in experimental setups requiring additional light sources for applications such as optogenetic stimulation.

Fitting sulfur dioxide (SO2) differential slant column densities (dSCDs) from multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of scattered sunlight is challenging because actinic light intensity is low in the wavelength regions where the SO2 absorption features are strongest. SO2 dSCDs were fit with different wavelength windows (λlow to λhigh) from ambient measurements with calibration cells of 2.2×1017 and 2.2×1016 molec. cm−2 inserted in the light path at different viewing elevation angles using an Ocean Optics USB2000 spectrometer in a miniature MAX-DOAS instrument. SO2 dSCDs were the least accurate, and fit errors were highest for fitting windows with λlow 312 nm. The SO2 dSCDs also exhibited an inverse relationship with the depth of the differential features in the SO2 absorption cross section for fitting windows with λlow 400 nm. Deviation of the SO2 dSCD from the true value depended on the SO2 concentration for some fitting windows rather than exhibiting a consistent bias. Uncertainties in the SO2 dSCD reported by the fit algorithm were more than 50 % less than the true error for many windows, particularly for the measurements without the filter or offset function. For retrievals with the filter or offset function, increasing λhigh > 320 nm tended to decrease the reported fit uncertainty but did not increase the accuracy. Based on the results of this study, a short-pass filter and a fitting window of 307.5

The aim of this study was to predict the critical nitrogen (N) content in peach trees using spectrometric measurements. A nutrient-controlled hydroponics experiment was designed for this purpose. Peach saplings were grown under three N conditions: deficient, sufficient, and excessive. The reflectance values of a plant leaves were measured using a handheld field spectroradiometer fitted with a plant probe. The N contents of leaves were determined in the laboratory and Gaussian mixture discriminant analysis (GMDA) was used to estimate N levels in the leaves from reflectance values. The N levels were categorized for each of the three different N conditions. The wavelengths at 425 nm, 574 nm, 696 nm, and 700 nm were found to be diagnostic of the different N levels. The model developed here classified the experimental plants with high accuracy for NDeficient, 89.28%; NSufficient, 96.30%; and NExcess, 71.42% with 85.71% coefficients. The reliability of the model was also tested under field conditions using 96 peach trees representing the three different N status. Leaves were analyzed by reflectance at 425 nm, 574 nm, 696 nm, and 700 nm, which functioned in real N, percentage classes determined based on the laboratory analyses of the orchard samples, and the data were categorized as NDeficient, NSufficient, and NExcess with a similarity ratio of 77.78%, 80%, and 67.74%, respectively with the general correct classification rate of 75%. The study findings showed that the model developed using hyperspectral reflectance data can discriminate different N nutritional status in plants with an accuracy of ≥70% and can be applied under field conditions. The results of this research provide a new perspective for future studies by showing that GMDA with hyperspectral remote sensing may be useful for the classification of different plant nutrient contents.

In the ultra-precision manufacturing of large optics, industrial robots have the potential to become an intelligent and economical choice of surface polishing. However, the transport of the workpieces between the polishing platform and the measurement instrument seriously limits the manufacturing efficiency. Therefore, an in-situ measurement system based on the monoscopic deflectometry is developed to determine the form quality of the optical lenses during rough polishing. Stray light reflected from the lower surface of transparent lenses may degrade the measuring quality, thus an effective absolute phase retrieval algorithm is developed to decouple the superposed fringes associated with the upper and lower surfaces. Then, the form of the upper surface under polishing can be reconstructed to guide the subsequent polishing. Experimental results demonstrate that the accuracy of the method is comparable to that of the coordinate measuring machine, consequently the manufacturing efficiency and reliability of large optical workpieces can be greatly improved.

Low angle dependence single green polystyrene colloidal crystal films were prepared by vertical deposition method using polystyrene microspheres with size of 380 ± 10 nm as raw material and further modified by adding nano-carbon. Without nano-carbon addition, the film showed various colors with changing the angle of incident light under natural light. With nano-carbon addition, saturation and angle dependence of the polystyrene colloidal crystal film were remarkably improved. With 0.01 wt % nano-carbon addition, since the stray light of other wavelengths other than the band gap light was absorbed by the added nano-carbon, the film showed only green color under different angles of incident light, suggesting that the film had low angle dependence. It is significant in the research of color behavior and is helpful to obtain single color polystyrene colloidal crystal film.

The interferometric signals produced in conventional dual-comb laser ranging require femtosecond lasers with long-term f_CEO stability, and are limited to an upper sampling rate by radio-frequency aliasing considerations. By using cross-polarized dual combs and two-photon detection we demonstrate carrier-phase-insensitive cross-correlations at sampling rates of up to 12x the conventional dual-comb aliasing limit, recording these in a digitizer-based acquisition system to implement ranging with sub-100-nm precision. We then extend this concept to show how the high data burden of conventional dual-comb acquisition can be eliminated by using a simple microcontroller as a ns-precision stopwatch to record the time intervals separating the two-photon cross-correlation pulses, providing real-time and continuous LiDAR-like distance metrology capable of sub-100 nm precision and dynamic acquisition for unlimited periods., Comment: 9 pages, 6 figures

Polarization-sensitive photodetectors are highly desirable for high-performance optical signal capture and stray light shielding in order to enhance the capability for detection and identification of targets in dark, haze, and other complex environments. Usually, filters and polarizers are utilized for conventional devices to achieve polarization-sensitive detection. Herein, to simplify the optical system, a two-dimensional self-powered polarization-sensitive photodetector is fabricated based on a stacked GeSe/MoS2 van der Waals (vdW) heterojunction which facilitates efficient separation and transportation of the photogenerated carriers because of type-II band alignment. Accordingly, a high-performance self-powered photodetector is achieved with merits of a very large on-off ratio photocurrent at zero bias of currently 104 and a high responsivity (Rλ) of 105 mA/W with an external quantum efficiency of 24.2%. Furthermore, a broad spectral photoresponse is extended from 380 to 1064 nm owing to the high absorption coefficient in a wide spectral region. One of the key benefits from these highly anisotropic orthorhombic structures of layered GeSe is self-powered polarization-sensitive detection with a peak/valley ratio of up to 2.95. This is realized irradiating with a 532 nm wavelength laser with which a maximum photoresponsivity of up to 590 mA/W is reached when the input polarization is parallel to the armchair direction. This work provides a facile route to fabricate self-powered polarization-sensitive photodetectors from GeSe/MoS2 vdW heterojunctions for integrated optoelectronic devices.

This paper presents a read-out integrated circuit (ROIC) for PM1, PM2.5, and PM10 airborne particle detector with a laser diode. The ROIC has a monitoring photodiode, which provides negative feedback through an automatic power control circuit. This adjusts the driving current to the laser diode, and thus stabilizes the illumination level. Offset compensation circuit in analog front-end eliminates the large offset voltage introduced by stray light reaching the measuring photodiode. A digital back-end analyses each pulse to determine the corresponding particle size, and also linearizes the response, which would otherwise drop off for smaller particles. The ROIC was fabricated in a $0.18~\mu \text{m}$ CMOS process. It has an area of 6.27 mm2 and draws 10 mW at 5 V. The ROIC is incorporated in a particle detector which is tested against an aerosol spectrometer. For particle concentrations up to $100~\mu \text{g}/\text{m}^{{3}}$ , this detector was found to have an accuracy of $\pm ~10~\mu \text{g}/\text{m}^{{3}}$ for PM10 and PM2.5, and $\pm ~15~\mu \text{g}/\text{m}^{{3}}$ for PM1. At higher concentrations, up to $1000~\mu \text{g}/\text{m}^{{3}}$ , the corresponding accuracies are ± 5 % and ± 10 %. Within the temperature range of 0 °C to 50 °C, the effective resolution of the detector changes only from 8.78 bits to 8.97 bits.

The method of image visibility detection is one of the methods closest to human vision. It is based on the principle of human eye observation but avoids the errors resulting from human subjectivity. However, the background and stray light and weather conditions seriously impact the detection. Furthermore, the inherent brightness contrast of the artificial target plate has a large error due to the reflection of the surface structure, which hinders the widespread application of this method. In this study, the effects of the gain and zero-drift errors and the measurement error from inherent brightness contrast on the measurement range and accuracy of atmospheric visibility are analyzed in detail. The detection baseline length is adaptively adjusted according to these errors to achieve the best detection.

A wide variety of plasma geometries and modalities have been utilized for chemical analysis to date, however, there is much left to be understood in terms of the underlying mechanisms. Plasma diagnostics have been used for many years to elucidate these mechanisms, with one of the most powerful techniques being laser scattering approaches. Laser scattering provides information about the energetic species distributions, in terms of kinetic energy and densities, which can provide invaluable insights into the fundamental processes of chemical analysis plasmas with minimal perturbation. Thomson scattering (TS) from free electrons is the most difficult to implement due to the extremely stringent instrumental requirements for discerning the signal from competing scatterers in low-density plasmas, such as those seen in analytical chemistry applications. Nonetheless, relatively few instruments have been developed to satisfy these stringent requirements. In this paper, the design and characterization of a transmission-type triple grating spectrograph (TGS), with high numerical aperture (0.25)/contrast (≤10−6 at 532 ± 0.5 nm)/stray light rejection (∼1.8 × 10−8 at 532 ± 22–32 nm) required for TS, will be presented. In addition, proof-of-principle measurements on glow discharges operated under typical optical emission spectroscopy (OES) conditions demonstrate the high light throughput and low limits-of-detection (∼109 cm−3 at ∼1 eV Te) afforded by the new instrument.

Ultrashort laser pulses in the femtosecond range are of growing interest in medicine and micro material processing for industrial applications. The most interesting parameter is the pulse duration, which can only be measured by optical autocorrelation methods incorporating an optically nonlinear medium. Established methods mostly use monocrystalline beta barium borate (BBO) in transmission, exhibiting a high nonlinear conversion efficiency. However, this material is brittle, expensive and sophisticated in adjustment due to the necessary non-collinear phase matching. Since fiber-based high energy femtosecond laser systems become more and more achievable, the conversion efficiency of the nonlinear medium should no longer be seen as the restricting factor. Therefore, this research work discusses the suitability of several nonlinear media with differing translucency. Quartz, ammonium dihydrogen phosphate (ADP) and aluminum nitride (AlN) were compared in a standard autocorrelation setup and a novel versatile setup measuring frequency-doubled stray light. Best results were achieved with AlN, which appears to be a suitable and promising alternative material to BBO, reducing the expenses by two to three orders of magnitude.

Dispersion problem has always constrained the development of see-through near-eye displays with diffractive waveguide. Here, we propose a design method and optical systems for achromatic surface microstructure composed with a triple-carved-sub-grating. The triple-carved-sub-grating with specified period is designed based on rigorous coupled wave theory, corresponding to Red, Green and Blue (RGB) wavelengths, respectively, with diffraction efficiencies of 1st(-1st) orders reach 47.5% under TE polarization. The surface microstructure with period of 18.9um is realized by integrating the three sub-gratings together, and it is verified numerically that the diffractive angle of RGB wavelengths is 35{\deg} and the crosstalk is less than 4.5% under the normal incidence of TE polarization, which imply the surface microstructure diffracts the certain RGB wavelengths achromatically. Via proper duplication it could be utilized as the combining optics of diffractive-waveguide near-eye display and head-up display because of its light and compact features., Comment: 5 pages, 1 figure

The fiber link between a telescope and a spectrograph is an attractive solution to improve the performance of astronomical instruments. The throughput of the observing system is mainly current concerned by the astronomer. The throughput of fiber link system is limited by the transmission efficiency (TE) and focal ratio degradation (FRD) of the fibers. The rapid measurement system for transmission characteristics of astronomical fibers (RMSTCAF) is an instrument to measure the output focal ratio (OFR), TE, the throughput of the fiber in a certain focal ratio and fiber endface quality. The number of optical fibers used in multi-object spectroscopy (MOS) and integral field spectroscopy (IFS) are increasing. It will be a time-consuming and huge burden to measure the FRD and TE of these fibers, especially the dynamic characteristics of high density optical cables. We designed this instrument to solve this problem. The system uses the encircled energy (EE) of the output energy of the fiber to determine the focal ratio of the optical fiber. With two measurement arms, the RMSTCAF provides feedback compensation to reducing the influence of incident light source fluctuation and realizes the closed-looped real-time measurement of the optical fiber transmission characteristics. The powermeters with double probes was used to suppress the environmental stray light to improve the measurement precision of the system with different wavelength. Used this system, we measured the critical focal ratio of the optical fiber with Numerical Aperture (NA) 0.128, the OFR average value within EE95 is F/3.83, compared with theoretical F critical /3.87, the error is 1.1%. We repeatedly connected the fiber with NA0.124 to the system and measured TE and OFR within EE90 and EE95. The standard deviation of them is 0.002, 0.03 and 0.02. As a universal measuring platform, RMSTCAF can meet the measurement requirements of minimum core diameter of 30 μ m, minimum incident focal ratio F/2.6 and wavelength range of 400–850 nm. It has good repeatability and environmental adaptability. It would provide effective data for the design and evaluation of astronomical instruments with fiber link.

Miniaturised photometric detection cell based on the 150 μm I. D. L-shaped fused silica capillary (L-cell) and silica optical fibre is discussed in this paper. Light enters the cell via right angle bend and transmitted light is collected by silica optical fibre inserted into the capillary outlet. Ray trace analysis reveals that L-cell geometry works as a waveguide and effectively eliminates parasitic light, which is guided by the wall of any fused silica capillary cell. Low total level of stray light is further documented by measurement of absorbance of acetone-water mixture at 266 nm with the observed upper limit of dynamic range 2.2 AU. 3-mm L-cell has a volume of 53 nL and exhibits effective optical path 2.7 mm. Cell variance determined in the flow rate range 1–10 μL min−1 indicates, that 3-mm L-cell is optimal for use with 200–300 μm I. D. capillary columns. Furthermore, isocratic separation of alkylbenzenes mixture at 0.5 μL min−1 demonstrates effective use of 0.5-mm L-cell (8.8 nL) and possible performance of longer L-cells with high efficiency 100 μm I. D. capillary column.

We present a way to prevent stray light generated from draft facets of Fresnel lens. Fresnel lens has distinctive shape that induces stray light. The draft facets can generate as much as 8% of stray light, deteriorating performance of optics. To prevent such stray light, we fabricated light-shielding film on draft facets and edges of Fresnel lens. First, we investigated structure and material of the shielding film. We then studied optimal laser source which can perform the precise processing, and found that laser ablation by picosecond laser works the best. Finally, we demonstrated the fabrication of light-shielding film on draft facets of Fresnel lens by experiment, and verified the elimination of stray light.

A method comprising near-field holography with an electron beam lithography-written phase mask was developed herein. Soft X-ray varied-line-spacing gratings with a central groove density greater than 3000 lines mm−1 were fabricated using this method., A fabrication method comprising near-field holography (NFH) with an electron beam lithography (EBL)-written phase mask was developed to fabricate soft X-ray varied-line-spacing gratings (VLSGs). An EBL-written phase mask with an area of 52 mm × 30 mm and a central line density greater than 3000 lines mm−1 was used. The introduction of the EBL-written phase mask substantially simplified the NFH optics for pattern transfer. The characterization of the groove density distribution and diffraction efficiency of the fabricated VLSGs indicates that the EBL–NFH method is feasible and promising for achieving high-accuracy groove density distributions with corresponding image properties. Vertical stray light is suppressed in the soft X-ray spectral range.

Well-defined Fe3O4@SiO2 composite colloidal particles decorated with Ag nanoparticles were successfully synthesized through a simple chemical approach. These particles self-assembled into 1D chain-like photonic structures under the induction of magnetic field and diffract tunable structural colors. The hue and brightness of the structural colors are related to Ag nanoparticles deposited on the particles surface and its brightness increases with the increase of Ag concentration. This phenomenon could be the result of the superposition of photonic bandgap formed by photonic crystals and possible plasmonic property, as well as capability in absorbing stray light of Ag nanoparticles. As-prepared Fe3O4@SiO2@Ag colloidal particles have great potential to be applied in many crucial areas such as color displaying, biological detection and anti-counterfeiting technology.

著者人数: 20名, Accepted: 2019-01-14, 資料番号: SA1180274000

A Thomson scattering (TS) system has been developed on Versatile Experiment Spherical Torus (VEST) to measure the electron temperature and the density. In VEST, it is quite challenging to measure TS signals because the energy of the utilized pulsed laser and the target electron density are low, 0.85 J and ∼5 × 1018 m−3, respectively. Furthermore, the difficulties caused by filter specifications have to be resolved because of the use of commercial interference filters with broad bandwidth and poor blocking at the laser wavelength. Therefore, we especially optimize the placement order of the filter sets based on the evaluation of the relative errors to overcome the poor spectral resolution. In addition, the amount of the stray light that penetrating filters is reduced by vacuum components such as baffles, louvres, and a viewing dump. With the careful installation and the optimization of the system, we can develop an efficient Thomson scattering system. Recently, TS signals have been successfully measured from the ohmic plasmas, and the electron temperature and the density are determined by analyzing the signals with the Bayesian method.

A new divertor Thomson scattering system has been developed for the MAST-U tokamak. The diagnostic will produce electron density and temperature profiles along the Super-X strike leg. The existing polychromator design has been adapted for low temperature measurements. A new 1061 nm channel with 2 nm bandwidth has been added to enable measurements down below the previous ∼5 eV limit on the core system. The optical filters used in the system have OD6 light rejection alongside a 1064.1 nm laser line filter to reduce stray light in the digitized channels. A new averaging technique has been applied to the scattered signal traces to improve the core Thomson data in the scrape-off layer. The technique reduces the systematic noise level in this region. This leads to a reduction in the error values for electron density and temperature measurements and, in particular, the digitizer noise. The technique has been applied to produce a radial profile for a number of L-mode MAST discharges down to very low densities of ∼1 × 1018 m−3.

EPIC (Earth Polychromatic Imaging Camera) raw level-0 (L0) data in one channel is a 12-bit 2048x2048 pixels image array plus auxiliary data such as telemetry, temperature readings, cloud, aerosol, ocean surface and vegetation properties, sulfur dioxide, etc. The EPIC L1a processor applies a series of correction steps on the L0 data to convert them into corrected count rates (level-1a or L1a data): Dark correction, Enhanced pixel detection, Read wave correction, Latency correction, Non-linearity correction, Temperature correction, Conversion to count rates, Flat fielding, and Stray light correction. L1a images should have all instrumental effects removed and only need to be multiplied by one single number for each wavelength to obtain radiances, which are the basis for all higher-level EPIC products, such as ozone and sulfur dioxide total column amounts, vegetation index, cloud, aerosol, ocean surface and vegetation properties, etc. This paper gives an overview of the mathematics and the pre-launch and on-orbit calibration behind each correction step.

The sidelobe phenomenon of acousto-optic tunable filter (AOTF)-based hyperspectral imaging is the result of the phase mismatching condition, which will reduce the quality of hyperspectral imaging data. This phenomenon can be observed in two specified scenes, namely, high brightness panchromatic target imaging and high brightness monochromatic target imaging. In this paper, the acousto-optic interaction in these two scenes is discussed using the phase matching condition. As a follow-up work of the previous related research, this paper studies laser interference in AOTF imaging, which is a typical example of the second case. A method to remove laser sidelobes in AOTF-based hyperspectral imaging is proposed, which combines a series of procedures including laser point extraction, reverse imaging before AOTF, ray tracing in AOTF, forward imaging process after AOTF, and laser elimination. Experimental results have verified the effectiveness of the proposed method.

CubeSats have been widely used in remote sensing applications such as global coverage, hotspots revisited, etc. However, due to the strict size limitation, the high-accuracy measuring instruments such as star tracker are too large to be applied in CubeSat, thus causing insufficient accuracy in satellite attitude and image positioning. In order to reduce the volume of star tracker without compromising the performance, the relationship between the volume and pointing accuracy or dynamic performance is studied and an optimization model of star tracker with a minimum volume is proposed. Compared with the traditional star tracker, a deployable star tracker with a novel deployable baffle and surrounded circuit structure is designed. The baffle consists of nested three-stage sub-baffles with a scientifically analyzed and verified taper to achieve smooth deployment and compression. The special circuit structure surrounds the lens and can be compressed in the inner sub-baffle. Therefore, the deployable star tracker can be compressed to the smallest volume and the sub-baffles can be deployed to the accurate position without self-lock risk. The experimental results verify its deployment accuracy and reliability as well as space environmental adaptability. The deployable star tracker has almost the same results on stray light suppression ability, pointing accuracy (better than 3″ (3σ)) and dynamic performance (up to 3°/s) with the traditional star tracker. Furthermore, an integrated attitude determination and control system based on the deployable star tracker for CubeSat is further designed and implemented to support high-accuracy remote sensing.

Off-axis three-mirror anastigmat (TMA) telescopes provide excellent correction of aberrations over a large field-of-view in one direction. In a push broom configuration, this lightweight and compact optical configuration enables high-performing imaging. Moreover, passive multi-spectral acquisition can be achieved using a filter stack positioned at the detector vicinity. Stray light is a typical limiting factor for instrument performance and its control is specific to the type of optical configuration. We describe the stray light control and analysis methods in an off-axis TMA. The design intends to control first-order scattering from non-optical surfaces and to block straight shots. This is achieved through usage of elements such as apertures and baffles, both internal and external to the instrument. It will be demonstrated that the aperture stop is a critical element, whose stray light contribution can be controlled with V-groove vanes. Impact of mirrors roughness, a manufacturing physical limitation, is evaluated by modeling the bidirectional scattering distribution function and computing the stray light distribution at the detector for point-like source illumination. We show that the scattering on the different mirrors broaden differently the spot size, as the successive mirrors focus or expand the scattered rays differently. Finally, the ghost reflections inside the filter stack are evaluated and we show that there is no cross-talk between the different channels.

Using 3D-printed n-faced pyramid lenses, we generate a series of structured diffraction free terahertz (THz) beams. Based on angular spectrum theory, analytical solutions of the output THz beams from these lenses can be obtained. Furthermore, we experimentally realize these non-diffraction THz beams, showing that the measured results are consistent with theory. It is believed that our structured non-diffraction THz beams can be used in THz imaging with large depth of focus.

The application range of hyperspectral imaging is subject to the operational system platform especially relies on the core imaging spectrometer. With a rising practical requirement of extensive remote sensing recently, the traditional method of two or multiple separate imaging submodules combined has obviously brought inevitable shortages in certain cases such as mineral detection or environmental monitoring, etc. Not only is the whole imaging system somewhat so large in physical size and so high in weight that it has an objective influence on convenience as well as flexibility in actual operation, but also each independent instrument has unique optical parameters and assembling matrices after fabrication and alignment which is against the image consistency. Instead of common image correction and data processing, the essential solution is to set up a broadband integrative system platform. This paper introduces a new prototype of imaging spectrometer in the visible and near-infrared (VNIR) to short-wave infrared (SWIR) region. Different from most existing research-based and commercial VNIR to SWIR imaging spectrometers, it is designed as broadband integration of a single core module. The main optical system consists of a collimating mirror, a central dispersive spherical prism, a converging mirror and two plane mirrors on the sides, which is similar to the normal convex grating spectrometer of three-concentric-mirror (Offner) configuration. The imaging spectrometer has relatively high imaging quality and satisfactory instantaneous field of view (IFOV) with a fairly compact internal structure benefiting from the integrated design and conscientious fabrication. The approach not only avoids extra expense and alignment complexities of multiple spectrometers but also enhances radiometric stability and reduces stray light and polarization effects. Relative performance tests are performed in various specific environment and validating imaging experiments are represented on schedule to demonstrate the expectant effectiveness of the whole system.

A new incoherent Thomson scattering system measures the evolution of electron velocity distribution functions perpendicular and parallel to the ambient magnetic field during kinking of a single flux rope and merging of two flux ropes through magnetic reconnection. The Thomson scattering system provides sub-millimeter spatial resolution, sufficient to diagnose the several millimeters sized magnetic reconnection electron diffusion region in the PHAse Space MAppgin experiment. Due to the relatively modest plasma density ∼1019 m−3 and electron temperature ∼1 eV, stray light suppression is critical for these measurements. Two volume Bragg gratings are used in series as a notch filter with a spectral bandwidth 47% is used as the detector in a 1.3 m spectrometer. Preliminary results of gun plasma electron temperature will be reported and compared with measurements obtained from a triple Langmuir probe.

Benefitting from the arbitrary and flexible light modulation, metasurface has attracted extensive attention and been demonstrated in different applications. However, most reported metasurface-based devices were normally composed of discrete micro or nano structures, therefore the discretization precision limited the performance of the device, including the focusing efficiency, stray light suppression, and broadband performance. In this work, an all-metallic reflective metasurface consisting of numerous quasi-continuous nanostructures is proposed to realize high-efficiency and broadband focusing. The constructed quasi-continuous metasurface (QCMS) is then verified numerically through electromagnetic simulation, and the numerical results show a higher focusing efficiency and a better stray light suppression effect, compared to a binary-phase-based metalens. Through the same design strategy, a QCMS with the ability to overcome the diffraction limit can also be constructed, and a focal spot with the size of 0.8 times the diffraction limit can be achieved. We expect that this quasi-continuous structure could be utilized to construct other high-performance devices that require continuous phase controls, such as the beam deflector, orbital angle momentum generator, and self-accelerating beam generator.

International audience; We present the polarimetric analysis of the white-light images of the corona obtained with the Large-Angle Spectrometric COronagraph LASCO-C3 onboard the Solar and Heliospheric Observatory (SOHO) from 1996 to 2019, leading to the separation of the K- and F-components and the derivation of the electron-density distribution. The analysis makes use of polarized sequences composed of three images obtained through three polarizers oriented at +60°, 0°, and -60°, complemented by a neighboring unpolarized image. However, the degradation of the 0° polarizer noticed in 1999 compelled us to reconstruct the corresponding images from those obtained with the two other polarizers and the unpolarized ones thereafter. The analysis closely follows the method developed for LASCO-C2 (Lamy et al. in Solar Phys. 295, 89, 2020) and implements the formalism of Mueller, albeit with additional difficulties notably the presence of a non-axially symmetric component of stray light. Critical corrections were derived from a SOHO roll sequence and from consistency criteria (e.g. the “tangential” direction of polarization). The quasi-uninterrupted photopolarimetric analysis of the outer corona over two complete Solar Cycles 23 and 24 was successfully achieved and our final results encompass the characterization of its polarization, of its polarized radiance, of the two-dimensional electron density, and of the K-corona. Comparison between the C3 and C2 results in the region where their fields of view overlap shows an overall agreement. The C3 results are further in agreement with those of eclipses and radio-ranging measurements to an elongation of ≈10 R⊙ but tend to diverge further out. Although the coronal polarization out to 20 R⊙ is still highly correlated with the temporal variation of the total magnetic field, this divergence probably results from the increasing polarization of the F-corona with increasing solar elongation.

International audience; Interferometry is often used as a means for providing high sensitivity measurements. But interferometric measurements can also be easily affected by coherent stray light. In many fields, a correct estimation of the amount of stray light is necessary to assess the system performances and to guide the choice of the correct design. The LISA (Laser Interferometer Space Antenna) mission will consist of three spacecraft orbiting the Sun in a triangle constellation with arms of 2.5 Mkm to detect gravitational waves. Detection is carried on thanks to two laser beams emitted by each spacecraft towards the two remote ones. A tiny fraction of the emitted beams is collected by the telescopes in the distant spacecrafts and interfered with the local laser beam, giving six heterodyne phase readouts which carry the imprint of the gravitational wave. Given the goal of reaching a noise floor of a few picometers on the distance measurement, this configuration will be very sensitive to stray light noise and for this reason stray light estimates are an important part of the design process. For a complex optical system stray light simulations can be made with specific optical analysis software (FRED, Zemax,...) which require expensive licences and computational time. To have a quick estimate one can try some manual calculation, but it is not always easy to find which scattering or reflection directions will lead to stray light able to couple into the interferometric measurement, not only with good superposition, but also with matching wavefront. We’ll use the divergence of the laser beam to estimate the angular aperture under which a scattering element in the optical system can direct stray light into a detector, and show how these simple considerations can lead to stray light estimates which are in good agreement with the most advanced software simulations. These considerations are applicable to various optical systems.

The optical properties of microlens arrays may be significantly affected by the optical crosstalk effect between adjacent lenses. Recently, this issue has triggered increasing attention in the scientific community. In this study, an integrated microlens array (MLA) consisting of self-aligning convergent waveguides of microlenses was fabricated. The optical crosstalk effect does not influence the performance of such system. Based on the self-focusing effect principle, self-writing of the waveguide array was achieved in a photosensitive polymer. The light collection and guiding performance of the MLA with and without thermal cross-linking treatment was analyzed in depth. The relation between the stray light and the filling rate of the MLA shows that a high filling rate decreases the optical crosstalk. Finally, an integrated MLA with a large area, high uniformity, and excellent optical performance was fabricated.

Recording the fluorescence of a magneto-optical trap (MOT) is a standard tool for measuring atom numbers in experiments with ultracold atoms. When trapping few atoms in a small MOT, the emitted fluorescence increases with the atom number in discrete steps, which allows one to measure the atom number with single-particle resolution. Achieving such single-particle resolution requires stringent minimization of stray light from the MOT beams, which is very difficult to achieve in experimental setups that require in-vacuum components close to the atoms. Here, we present a modified scheme that addresses this issue: Instead of collecting the fluorescence on the MOT (D2) transition, we scatter light on an additional probing (D1) transition and collect this fluorescence with a high-resolution microscope while filtering out the intense MOT light. Using this scheme, we are able to reliably distinguish up to 17 $^{40}\mathrm{K}$ atoms with classification fidelities of $\ensuremath{\sim}98%$ for up to 5 atom numbers and fidelities of more than 85% for up to 17 atoms.

We have developed an SI-traceable narrow-band tunable radiance source based on an optical parametric oscillator (OPO) and an integrating sphere for the calibration of spectroradiometers. The source is calibrated with a reference detector over the ultraviolet/visible spectral range with an uncertainty of < 1 % . As a case study, a CubeSat spectroradiometer has been calibrated for radiance over its operating range from 370 nm to 480 nm. To validate the results, the instrument has also been calibrated with a traditional setup based on a diffuser and an FEL lamp. Both routes show good agreement within the combined measurement uncertainty. The OPO-based approach could be an interesting alternative to the traditional method, not only because of reduced measurement uncertainty, but also because it directly allows for wavelength calibration and characterization of the instrumental spectral response function and stray light effects, which could reduce calibration time and cost.

Light absorption by the water column plays an important role in the spatial and temporal distribution of light attenuation, mixed layer heating, primary productivity, and phytoplankton biomass in the water column. The absorption properties of water components are the main influences of the underwater light field and surface spectrum. The study of the absorption properties of the water body contributes to the understanding of its optical properties and the remote sensing inversion of water quality parameters. The effects of light source polarization on the spectral absorption coefficient measurements of colored dissolved organic matter (CDOM) and total particulate matter (TPM) in water were investigated by measuring the polarization of the light source in a UV-Vis spectrophotometer. The results show that the light source of the UV-Vis spectrophotometer is significantly polarized, but the effect of the polarization of the light source on the measurement of the spectral absorption coefficients of CDOM and TPM in water is very small and almost negligible.

We report on a joule-level, 1047 nm Nd:YLF master oscillator power amplifier laser with near-diffraction-limited beam quality. The master oscillator and two-stage two-pass amplifier were all-flashlamp-pumped. The laser produced 2 J output pulses with 3 ns duration at 10 Hz pulse repetition rate. High beam quality was achieved by using a liquid stimulated Brillouin scattering mirror and additional astigmatism compensation.

Pupil expansion using waveguide propagation and pupil replication has been a popular method of developing head-up displays and near-to-eye displays. This paper examines one of the limits of pupil replication, which involves projecting images at a finite distance through a single waveguide by holographic optical elements and seeing the image doubling artifact. A Zemax model and a demonstrator were developed to determine the cause of image doubling. A relationship between the designed outcoupled image distance of a waveguide, pupil size, optical path length, and angle of image doubling is established. In waveguide pupil replication, the internally propagating light should be close to collimated to mitigate image doubling. We also provide a solution to project the image at different distances, which is an important factor for some applications, such as automotive head-up display and the seamless integration of augmented reality information with the natural environment.

We demonstrate an interferometric method to provide direct, single-shot measurements of cavitation bubble dynamics with nanoscale spatial and temporal resolution with results that closely match theoretical predictions. Implementation of this method reduces the need for expensive and complex ultra-high speed camera systems for the measurement of single cavitation events. This method can capture dynamics over large time intervals with sub-nanosecond temporal resolution and spatial precision surpassing the optical diffraction limit. We expect this method to have broad utility for examination of cavitation bubble dynamics, as well as for metrology applications such as optorheological materials characterization. This method provides an accurate approach for precise measurement of cavitation bubble dynamics suitable for metrology applications such as optorheological materials characterization.

For higher detection capability, dual band/dual field of view (FOV) infrared imaging systems are often used to recognize camouflaged targets. In this Letter, we report a dual band/dual FOV infrared imaging system with freeform prism, in which the optical path is folded drastically. Each spectral band will pass through the same entrance pupil and then is split off by a beam splitter so that each spectral band can match a different FOV. Compared to traditional infrared imaging systems, the proposed system has advantages of less volume, higher integration, and optical efficiency.

Various instrumental or geophysical artifacts, such as saturation, stray light or obstruction of light (either coming from the instrument or related to solar eclipses), negatively impact satellite measured ultraviolet and visible Earthshine radiance spectra and downstream retrievals of atmospheric and surface properties derived from these spectra. In addition, excessive noise such as from cosmic-ray impacts, prevalent within the South Atlantic Anomaly, can also degrade satellite radiance measurements. Saturation specifically pertains to observations of very bright surfaces such as sunglint over open water or thick clouds. When saturation occurs, additional photoelectric charge generated at the saturated pixel may overflow to pixels adjacent to a saturated area and be reflected as a distorted image in the final sensor output. When these effects cannot be corrected to an acceptable level for science-quality retrievals, flagging of the affected pixels is indicated. Here, we introduce a straightforward detection method that is based on the correlation, r, between the observed Earthshine radiance and solar irradiance spectra over a 10 nm spectral range; our decorrelation index (DI for brevity) is simply defined as a DI of 1−r. DI increases with anomalous additive effects or excessive noise in either radiances, the most likely cause in data from the Ozone Monitoring Instrument (OMI), or irradiances. DI is relatively straightforward to use and interpret and can be computed for different wavelength intervals. We developed a set of DIs for two spectral channels of the OMI, a hyperspectral pushbroom imaging spectrometer. For each OMI spatial measurement, we define 14 wavelength-dependent DIs within the OMI visible channel (350–498 nm) and six DIs in its ultraviolet 2 (UV2) channel (310–370 nm). As defined, DIs reflect a continuous range of deviations of observed spectra from the reference irradiance spectrum that are complementary to the binary saturation possibility warning (SPW) flags currently provided for each individual spectral or spatial pixel in the OMI radiance data set. Smaller values of DI are also caused by a number of geophysical factors; this allows one to obtain interesting physical results on the global distribution of spectral variations.

While meteorological numerical models extend upward to the mesopause, mesospheric observations are required for leading simulations and numerical weather forecasts and climate projections. This work reviews some of the challenges about temperature observation requirements and the limiting factors of the actual measurements associated with atmospheric tides. A new strategy is described here using a limb-scattering technique that is based on previous experiments in space. Such observations can be used with cube satellites. Technical issues are the large dynamic range (4 orders of magnitude) required for the measurements, the accuracy of the limb pointing, and the level of stray light. The technique described here will expect accuracy of 1–2 K with a vertical resolution of 1–2 km. A constellation of 100 platforms could provide temperature observations with space (100 km) and time (3 h) resolutions recommended by the World Meteorological Organization, and tidal issues could be resolved with a minimum of 3–5 platforms with specific orbit maintained to avoid drifts.

High-contrast imaging enabled by a starshade in formation flight with a space telescope can provide a near-term pathway to search for and characterize temperate and small planets of nearby stars. NASA's Starshade Technology Development Activity to TRL5 (S5) is rapidly maturing the required technologies to the point at which starshades could be integrated into potential future missions. Here we reappraise the noise budget of starshade-enabled exoplanet imaging to incorporate the experimentally demonstrated optical performance of the starshade and its optical edge. Our analyses of stray light sources - including the leakage through micrometeoroid damage and the reflection of bright celestial bodies - indicate that sunlight scattered by the optical edge (i.e., the solar glint) is by far the dominant stray light. With telescope and observation parameters that approximately correspond to Starshade Rendezvous with Roman and HabEx, we find that the dominating noise source would be exozodiacal light for characterizing a temperate and Earth-sized planet around Sun-like and earlier stars and the solar glint for later-type stars. Further reducing the brightness of solar glint by a factor of 10 with a coating would prevent it from becoming the dominant noise for both Roman and HabEx. With an instrument contrast of 1E-10, the residual starlight is not a dominant noise; and increasing the contrast level by a factor 10 would not lead to any appreciable change in the expected science performance. If unbiased calibration of the background to the photon-noise limit can be achieved, Starshade Rendezvous with Roman could provide nearly photon-limited spectroscopy of temperate and Earth-sized planets of F, G, and K stars, Accepted for publication in the Journal of Astronomical Telescopes, Instruments, and Systems (JATIS)

Traditional approach to stray light characterization is intrinsically limited. While the stray light level in an optical instrument can be measured, it is not possible to derive from experimental measurements the origin of the different features. Consequently, when unexpectedly high stray light is present, it is extremely difficult to find how to improve the system. In this paper, we introduce a new method where a pulsed laser and an ultra-fast sensor is used. As different stray light contributors have different optical path lengths, they reach the detector at different times and resolving them temporally allows to measure them separately. Their origin can be retrieved by using the optical path length as a mean of identification. We present the conceptual study and the experimental proof of concept of this new method. We were able to characterize individually the different stray light components in an imaging system and determine their origin. We show how the measurements allow to reverse engineer the instrument properties and even verify sub-system requirements.

In this study, a model is proposed to design and manage the stray light of a compact final optics assembly (FOA) for a high energy laser system. Based on the method we proposed, the high-order stray light can be managed to optimizing the position and angle of the optical elements. A light trap is designed to manage the first-order stray light with high fluence. Applying the method, we provide an experimental demonstration to designing a compact FOA. By comparing the cleaning results with no management testing result, it proves that using the above design and management, it can achieve the great improvement of cleanliness from ISO Class 5 to Class 3, which is significant to improve the output capability of the high energy laser system. In addition, we also verify the stray light by an optical field paper. It demonstrates that the field characteristics and position calculation of stray light are reliable.

We present geometrical and physical optics simulation results for the Simons Observatory Large Aperture Telescope. This work was developed as part of the general design process for the telescope; allowing us to evaluate the impact of various design choices on performance metrics and potential systematic effects. The primary goal of the simulations was to evaluate the final design of the reflectors and the cold optics which are now being built. We describe non-sequential ray tracing used to inform the design of the cold optics, including absorbers internal to each optics tube. We discuss ray tracing simulations of the telescope structure that allow us to determine geometries that minimize detector loading and mitigate spurious near-field effects that have not been resolved by the internal baffling. We also describe physical optics simulations, performed over a range of frequencies and field locations, that produce estimates of monochromatic far field beam patterns which in turn are used to gauge general optical performance. Finally, we describe simulations that shed light on beam sidelobes from panel gap diffraction., 15 pages, 13 figures