Deep Learning Models to Reduce Stray Light in TJ-II Thomson Scattering Diagnostic.

Nuclear fusion is a potential source of energy that could supply the growing needs of the world population for millions of years. Several experimental thermonuclear fusion devices try to understand and control the nuclear fusion process. A very interesting diagnostic called Thomson scattering (TS) is performed in the Spanish fusion device TJ-II. This diagnostic takes images to measure the temperature and density profiles of the plasma, which is heated to very high temperatures to produce fusion plasma. Each image captures spectra of laser light scattered by the plasma under different conditions. Unfortunately, some images are corrupted by noise called stray light that affects the measurement of the profiles. In this work, we propose the use of deep learning models to reduce the stray light that appears in the diagnostic. The proposed approach utilizes a Pix2Pix neural network, which is an image-to-image translation based on a generative adversarial network (GAN). This network learns to translateimages affected by stray light to images without stray light. This allows for the effective removal of the noise that affects the measurements of the TS diagnostic, avoiding the need for manual image processing adjustments. The proposed method shows a better performance, reducing the noise up to 98% inimages, which surpassesprevious works that obtained 85% for the validation dataset.

Analysis and Suppression Design of Stray Light Pollution in a Spectral Imager Loaded on a Polar-Orbiting Satellite.

As the non-imaging light of optical instruments, stray light has an important impact on normal imaging and data quantification applications. The FY-3D Medium Resolution Spectral Imager (MERSI) operates in a sun-synchronous orbit, with a scanning field of view of 110° and a surface imaging width of more than 2300 km, which can complete two coverage observations of global targets per day with high detection efficiency. According to the characteristics of the operating orbit and large-angle scanning imaging of MERSI, a stray light radiation model of the polar-orbiting spectrometer is constructed, and the design requirements of stray light suppression are proposed. Using the point source transmittance (PST) as the merit function of the stray light analysis method, the instrument was simulated with all stray light suppression optical paths, and the effectiveness of stray light elimination measures was verified using the stray light test. In this paper, the full-link method of "orbital stray light radiation model-system, internal and external simulation design-system analysis and actual test comparison verification" is proposed, and there is a maximum decrease in the system's PST by about 10 times after applying the stray light suppression's optimization design, which can provide a general method for stray light suppression designs for polar-orbit spectral imagers.

Stray Light Analysis and Suppression of the Visible to Terahertz Integrated Cloud Detection Optical System.

The wide-spectrum integrated imaging method can simultaneously obtain the spectral information of different spectral bands of the same target, which is conducive to the realization of the high-precision detection of target characteristics, and can simultaneously obtain more comprehensive elements such as the structure, shape, and microphysical parameters of the cloud. However, for stray light, the same surface has different characteristics at different wavelengths, and a wider spectral band means more complex and diverse sources of stray light, which renders the analysis and suppression of stray light more difficult. In this work, according to the characteristics of the visible-to-terahertz integrated optical system design scheme, the influence of material surface treatment on stray light was studied; the stray light analysis and optimization of the whole link of light transmission were carried out. For the sources of stray light in different channels, targeted suppression measures such as front baffle, field stop, special structure baffle, and reflective inner baffle were adopted. The simulation results indicate that when the off-axis field of view was greater than 10°. The point source transmittance (PST) of the terahertz channel is on the order of 10-4, the visible and infrared channels are less than 10-5, and the final terahertz PST was on the order of 10-8, while visible and infrared channels were lower than 10-11. Here, we present a method for stray light suppression based on conventional surface treatments for broadband imaging systems.

Estimation of Lens Stray Light with Regard to the Incapacitation of Imaging Sensors-Part 2: Validation.

Recently, we developed a simple theoretical model for the estimation of the irradiance distribution at the focal plane of commercial off-the-shelf (COTS) camera lenses in case of laser illumination. The purpose of such a model is to predict the incapacitation of imaging sensors when irradiated by laser light. The model is based on closed-form equations that comprise mainly standard parameters of the laser dazzle scenario and those of the main devices involved (laser source, camera lens and imaging sensor). However, the model also includes three non-standard parameters, which describe the scattering of light within the camera lens. In previous work, we have performed measurements to derive these typically unknown scatter parameters for a collection of camera lenses of the Double-Gauss type. In this publication, we compare calculations based on our theoretical model and the measured scatter parameters with the outcome of stray light simulations performed with the optical design software FRED in order to validate the reliability of our theoretical model and of the derived scatter parameters.

Analysis of Stray Light and Enhancement of SNR in DMD-Based Spectrometers.

Due to advantages such as the high efficiency of light utilization, small volume, and vibration resistance, digital micro-mirror device (DMD)-based spectrometers are widely used in ocean investigations, mountain surveys, and other field science research. In order to eliminate the stray light caused by DMDs, the stray light in DMD-based spectrometers was first measured and analyzed. Then, the stray light was classified into wavelength-related components and wavelength-unrelated components. Moreover, the noise caused by the stray light was analyzed from the perspective of encoding equation, and the de-noising decoding equation was deduced. The results showed that the accuracy range of absorbance was enhanced from [0, 1.9] to [0, 3.1] in single-stripe mode and the accuracy range of absorbance was enhanced from [0, 3.8] to [0, 6.3] in Hadamard transform (HT) multiple-stripe mode. A conclusion can be drawn that the de-noising strategy is feasible and effective for enhancing the SNR in DMD-based spectrometers.

Research on Stray-Light Suppression Method for Large Off-Axis Three-Mirror Anastigmatic Space Camera.

The stray-light suppression of a large off-axis three-mirror anastigmatic space camera has been a hot topic, and this study proposes a composite stray-light suppression strategy that effectively suppresses stray light using the combination of a baffle, retaining ring, and internal antistray light measures. Additionally, the light barrier of the third mirror with a three-layered structure was designed to further optimize the composite stray-light suppression system. At the stray-light simulation analysis stage, in view of the limitations of the Torrance-Sparrow scattering analysis model, an analysis model with wide adaptability is proposed, which can be applied to the stray-light simulation analysis of large-size mirrors with rough surfaces. The simulation results indicate that the point source transmittance of the composite stray-light suppression strategy proposed in this paper is of the order of 10-5 before installing the light barrier of the third mirror, and the veiling glare index of the full field of view is less than 5.8%. After installing the light barrier of the third mirror, the point source transmittance reached the order of 10-8, and the veiling glare index of the full field of view was less than 1.31%. Moreover, the influence of the light barrier of the third mirror on the modulation transfer function of the system was less than 2.3%. The modulation transfer function test of the large-width off-axis three-mirror anastigmatic space camera in a simulated vacuum on-orbit environment was completed, and the test results indicated that the negative impact of the light barrier of the third mirror on the modulation transfer function was less than 3.6%. Moreover, an out-of-field imaging test of the space camera was conducted and the results showed that the image was clear, and the SNR reached 80 dB. The simulation and experimental results prove that the solution in this study can effectively solve the problem of stray-light suppression for large off-axis three-mirror anastigmatic space cameras.

Estimation of Lens Stray Light with Regard to the Incapacitation of Imaging Sensors.

We present our efforts on estimating light scattering characteristics from commercial off-the-shelf (COTS) camera lenses in order to deduce thereof a set of generic scattering parameters valid for a specific lens class (double Gauss lenses). In previous investigations, we developed a simplified theoretical light scattering model to estimate the irradiance distribution in the focal plane of a camera lens. This theoretical model is based on a 3-parameter bidirectional scattering distribution function (BSDF), which describes light scattering from rough surfaces of the optical elements. Ordinarily, the three scatter parameters of the BSDF are not known for COTS camera lenses, which makes it necessary to assess them by own experiments. Besides the experimental setup and the measurement process, we present in detail the subsequent data exploitation. From measurements on seven COTS camera lenses, we deduced a generic set of scatter parameters. For a deeper analysis, the results of our measurements have also been compared with the output of an optical engineering software. Together with our theoretical model, now stray light calculations can be accomplished even then, when specific scatter parameters are not available from elsewhere. In addition, the light scattering analyses also allow considering the glare vulnerability of optical systems in terms of laser safety.

Analysis and Reduction of Solar Stray Light in the Nighttime Imaging Camera of Luojia-1 Satellite.

As one of the experimental payloads on Luojia-1 satellite, the nighttime imaging camera works with a high sensitivity to acquire nighttime light on earth. Solar stray light is a fatal problem for optical satellite works in the polar orbit, even for nighttime scene imaging, resulting in image saturation and light signal detection failure. To solve this problem, an analysis of the range of solar incident angles was conducted firstly. Based on the result, a special-shaped baffle was designed to avoid direct sunlight incidence. Moreover, the capability of stray light elimination of the lens was enhanced by an order of magnitude via optimizing the internal structure. An evaluation of secondary scattering stray lights into the camera from surrounding parts was performed based on a real satellite model. The results showed that the stray light elimination reaches a 10-10 order, meeting design requirements. Utilizing on-orbit images, the ability of satellites in illuminated areas to obtain artificial lights in dawn-dusk area was verified, proving the effectiveness of the stray light elimination design.

Compact photometric detector integrated with separation microchip for potential portable liquid chromatography system.

In recent years, miniaturized analytical instruments have been developing to meet the needs of portable and rapid analysis. The key of miniaturized analytical equipment is the miniaturization and integration of functional modules. This paper aims to develop a miniaturized photometric detector and separation microfluidic chip for a liquid chromatography (LC) system. The detector uses a light-emitting diode to emit ultraviolet light, which is collimated by an internal double lens. A Z-shaped flow cell with a long optical path is designed and fabricated in the separation microfluidic chip with a three-layer structure, which provides a tubing-free connection between the separation and detection unit. Detector performance is evaluated using hemoglobin (Hb) samples, with an upper limit of detection linearity (95 %) of 0.345 AU and stray light level as low as 0.08 %. Additionally, the microchip channel can be filled with cation exchange resin and C18 particles. Finally, an ion LC system and a reversed-phase LC system were constructed based on the miniaturized photometric detector and two microchips with different packed columns, respectively, and were successfully used in the separation and detection of two metabolic markers (glycated hemoglobin or bilirubin). The results of this study are expected to facilitate the development of a portable LC system and their application in community health services and family health management of chronic diseases.

Analysis and Suppression of Crosstalk Stray Light in a Microlens Array Scanning and Searching System.

The microlens array (MLA) system can aid in realizing fast beam deflection owing to the lateral displacement between arrays. The MLA system has the advantages of miniaturization and good functionality. However, during system operation, crosstalk beams are generated between each microlens array unit, introducing additional stray light, thus affecting the imaging contrast of the system. Therefore, this study uses the matrix operation method to trace the paraxial ray to trace the optical system and analyzes the generation mechanism of crosstalk stray light in the MLA system. Furthermore, this study proposes a crosstalk suppression method based on a stop array to reasonably suppress stray light. Finally, an example of an infrared array scanning infrared optical system is considered so as to verify the correctness and feasibility of the proposed crosstalk stray light suppression method. Therefore, this paper introduces the stray light suppression principle to guide the optical design process of the system, providing a theoretical basis for the design and analysis of the microlens array scanning and search system.

An improved design of the fused silica capillary flow cell for absorbance detection in microcolumn liquid chromatography.

Efficient absorbance detection of a low-volume chromatography peak is a difficult task. In this work, an improved design of the fused silica capillary flow cell for absorbance detection in microcolumn liquid chromatography is described. The cell was fabricated from 0.15 mm I. D. fused silica capillary and silica optical fibres. Optical fibres were fully integrated into the cell design and enabled a convenient and effective connection of the cell with the light source and light detector (265 nm UV LED and photodiode in this work). Manufactured cells covered the range of physical lengths 3.1-9.9 mm (55-175 nL) and were used without any focusing optics and slits. Baseline noise was typically below 0.05 mAU and the effective optical path determined in the experiments was 83-97% of the cell's physical length. The level of stray (parasitic) light indicated by a 1% deviation from linearity at 1.7 AU was 0.08% only. The proposed cell design was found to be moderately susceptible to the refractive index change (20-35 mAU baseline change in 5-95% (v/v) gradient of acetonitrile or methanol in a mixture with water, G index up to 4 AU·s/RIU). Manufactured cells were finally applied for absorbance detection of components of test the mixture eluted off 0.3 mm I. D. microcolumn. 9.9 mm cell (175 nL) with an effective optical path of 8.9 mm exhibited contribution to the broadening of chromatography peak comparable with commercial 6 mm (80 nL) rectangular flow cell.

Forward Light Scattering of First to Third Generation Vitreous Body Replacement Hydrogels after Surgical Application Compared to Conventional Silicone Oils and Vitreous Body.

To treat certain vitreoretinal diseases, the vitreous body, a hydrogel composed of mostly collagen and hyaluronic acid, must be removed. After vitrectomy surgery, the vitreous cavity is filled with an endotamponade. Previously, pre-clinical hydrogel-based vitreous body substitutes either made from uncrosslinked monomers (1st generation), preformed crosslinked polymers (2nd generation), or in situ gelating polymers (3rd generation) have been developed. Forward light scattering is a measure of Stray light induced by optical media, when increased, causing visual disturbance and glare. During pinhole surgery, the hydrogels are injected into the vitreous cavity through a small 23G-cannula. The aim of this study was to assess if and to what extent forward light scattering is induced by vitreous body replacement hydrogels and if Stray light differs between different generations of vitreous body hydrogel replacements due to the different gelation mechanisms and fragmentation during injection. A modified C-Quant setup was used to objectively determine forward light scattering. In this study, we found that the 1st and 3rd generation vitreous body replacements show very low stray light levels even after injection (2.8 +/- 0.4 deg2/sr and 0.2 +/- 0.2 deg2/sr, respectively) as gel fragmentation and generation of interfaces is circumvented. The 2nd generation preformed hydrogels showed a permanent increase in stray light after injection that will most likely lead to symptoms such as glare when used in patients (11.9 +/- 0.9 deg2/sr). Stray light of the 2nd generation hydrogels was 3- and 2-fold increased compared to juvenile and aged vitreous bodies, respectively. In conclusion, this significant downside in the forward light scattering of the 2nd generation hydrogels should be kept in mind when developing vitreous body replacement strategies, as any source of stray light should be minimized in patients with retinal comorbidities.

Corrigendum: The Influence of the Stimulus Design on the Harmonic Components of the Steady-State Visual Evoked Potential.

[This corrects the article DOI: 10.3389/fnhum.2020.00343.].

The Influence of the Stimulus Design on the Harmonic Components of the Steady-State Visual Evoked Potential.

Steady-state visual evoked potentials (ssVEPs) are commonly used for functional objective diagnostics. In general, the main response at the stimulation frequency is used. However, some studies reported the main response at the second harmonic of the stimulation frequency. The aim of our study was to analyze the influence of the stimulus design on the harmonic components of ssVEPs. We studied 22 subjects (8 males, mean age ± SD = 27 ± 4.8 years) using a circular layout (r 1 = 0-1.6°, r 2 = 1.6-3.5°, r 3 = 3.5-6.4°, r 4 = 6.4-10.9°, and r 5 = 10.9-18°). At a given eccentricity, the stimulus was presented according to a 7.5 Hz square wave with 50% duty cycle. To analyze the influence of the stimulus eccentricity, a background luminance of 30 cd/m2 was added to suppress foveal stray light effects; to analyze the influence of simultaneous foveal and peripheral stimulations, stimulations are performed without stray light suppression. For statistical analysis, medians M of the amplitude ratios for amplitudes at the second harmonic to the first harmonic and the probability of the occurrence of the main response at the second harmonic P(MCSH) are calculated. For stimulations with foveal stray light suppression, the medians were M 0 -1.6^ ∘ = 0.45, M 1.6 -3.5^ ∘ = 0.45, M 3.5 -6.4^ ∘ = 0.76, M 6.4 -10.9^ ∘ = 0.72, and M 10.9 -18^ ∘ = 0.48, and the probabilities were P 0-1.6^ ∘ (MCSH) = 0.05, P 1.6 -3.5^ ∘ (MCSH) = 0.05, P 3.5 -6.4^ ∘ (MCSH) = 0.32, P 6.4 -10.9^ ∘ (MCSH) = 0.29, and P 10.9 -18^ ∘ (MCSH) = 0.30. For stimulations without foveal stray light suppression, the medians M were M 0 -1.6^ ∘ = 0.29, M 1.6 -3.5^ ∘ = 0.37, M 3.5 -6.4^ ∘ = 0.98, M 6.4 -10.9 ^^ ∘ = 1.08, and M 10.9 -18^ ∘ = 1.24, and the probabilities were P 0-1.6^ ∘ (MCSH) = 0.09, P 1.6 -3.5^ ∘ (MCSH) = 0.05, P 3.5 -6.4^ ∘ (MCSH) = 0.50, P 6.4 -10.9^ ∘ (MCSH) = 0.55, and P 10.9 -18^ ∘ (MCSH) = 0.55. In conclusion, the stimulus design has an influence on the harmonic components of ssVEPs. An increase in stimulation eccentricity during extrafoveal stimulation leads to a transition of the main response to the second harmonic. The effect is enhanced by a simultaneous foveal stimulation.

The Improvement on the Performance of DMD Hadamard Transform Near-Infrared Spectrometer by Double Filter Strategy and a New Hadamard Mask.

In the Hadamard transform (HT) near-infrared (NIR) spectrometer, there are defects that can create a nonuniform distribution of spectral energy, significantly influencing the absorbance of the whole spectrum, generating stray light, and making the signal-to-noise ratio (SNR) of the spectrum inconsistent. To address this issue and improve the performance of the digital micromirror device (DMD) Hadamard transform near-infrared spectrometer, a split waveband scan mode is proposed to mitigate the impact of the stray light, and a new Hadamard mask of variable-width stripes is put forward to improve the SNR of the spectrometer. The results of the simulations and experiments indicate that by the new scan mode and Hadamard mask, the influence of stray light is restrained and reduced. In addition, the SNR of the spectrometer also is increased.

Comparison of ring 1 parameters in 37-segment multifocal electroretinography between onset and offset conditions of ring 2 to 4 in normal subjects.

AIM: To investigate whether the response of a central hexagonal element corresponding to the macular area in conventional multifocal electroretinography (mfERG) tests was the same as that of experimental mfERG using single central hexagonal element stimulation. METHODS: Prospective, observational study. Thirty healthy subjects were included in this study. mfERG recordings were performed according to two protocols: stimulus with 37 hexagonal elements (protocol 1), and stimulus with a single central element created by deactivating the other 36 hexagonal elements (protocol 2). We compared differences between ring 1 parameters in each protocol. RESULTS: In protocol 1, the first positive component (P1) implicit time and P1 amplitude were 37.8±1.8ms and 6.3±2.7 µV. After single element stimulation (protocol 2), double positive waves appeared. The implicit time and amplitude of P1 were 40.7±2.4ms (P<0.001) and 9.1±3.3 µV (P=0.001), respectively. The implicit time and amplitude of the second positive component (P2) were 68.0±4.5ms (P<0.001, compared with P1 in protocol 1) and 12.3±4.7 µV (P<0.001, compared with P1 in protocol 1), respectively. The amplitude of P2 in protocol 2 was about two times higher than that of P1 in protocol 1. CONCLUSION: mfERG responses of a central hexagonal element in a single element stimulation protocol are different from those of multiple element stimulation. The positive wave is more enhanced compared to that of the conventional protocol and it elongated into two wavelets.

Nanolitre-scale cell based on L-shaped silica capillary and optical fibre for absorption photometric detection in capillary liquid chromatography.

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.

[Cut-off filter : Physical and physiological basics]. / Kantenfilter : Physikalische und physiologische Grundlagen.

Light filters with wavelength-dependent transmission and in particular cut-off or step filters (steep dependence of transmission on wavelength) have a broad optical application and are relevant in ophthalmology. This article describes some physical and physiological principles of cut-off filters, discusses the physiological aspects of applications, specifically the not always relevant necessity of blue-reducing filters and the lack of efficacy of color filters with color vision deficiencies.

Light scattering in the human eye modelled as random phase perturbations.

Light scattering in the eye affects the quality of vision and its effect increases with aging and related pathologies, such as cataracts. Simulating methods were developed in order to reproduce the effects of this phenomenon. We introduce a statistical model of wavefront perturbations at the pupil plane of the eye that replicates the characteristic angular distribution of the light distribution over the retina. Our approach is based on the parameterization of the discrete cosine spectrum of the wavefront perturbation. The model performance was experimentally validated with a dedicated setup using a liquid crystal on silicon device as a spatial phase modulator. This instrument can be used for further visual experiments with controlled induction of light scattering.

System based on the contrast of Purkinje images to measure corneal and lens scattering.

Current methods to measure intraocular scattering provide information on the total scattered light, which consists of the combined contributions originating from different ocular structures. In this work, we propose a technique for the objective and independent assessment of scattering caused by the cornea and the lens based on the analysis of the contrast of the third and fourth Purkinje images. The technique is preliminarily validated first by using artificial eyes with different levels of corneal and lens scattering; second, it is validated in eyes wearing customized contact lenses to simulate corneal scattering and eyes with nuclear cataracts. Finally, it is tested on a larger population of eyes with cataracts and corneal disorders to prove its clinical usefulness.