Spectral Sensitivity Research Articles

Spectral Reflectance Estimation from Camera Response Using Local Optimal Dataset and Neural Networks.

In this study, a novel method is proposed to estimate surface-spectral reflectance from camera responses that combine model-based and training-based approaches. An imaging system is modeled using the spectral sensitivity functions of an RGB camera, spectral power distributions of multiple light sources, unknown surface-spectral reflectance, additive noise, and a gain parameter. The estimation procedure comprises two main stages: (1) selecting the local optimal reflectance dataset from a reflectance database and (2) determining the best estimate by applying a neural network to the local optimal dataset only. In stage (1), the camera responses are predicted for the respective reflectances in the database, and the optimal candidates are selected in the order of lowest prediction error. In stage (2), most reflectance training data are obtained by a convex linear combination of local optimal data using weighting coefficients based on random numbers. A feed-forward neural network with one hidden layer is used to map the observation space onto the spectral reflectance space. In addition, the reflectance estimation is repeated by generating multiple sets of random numbers, and the median of a set of estimated reflectances is determined as the final estimate of the reflectance. Experimental results show that the estimation accuracies exceed those of other methods.

Lead-free Cs3Bi2I9 perovskite hexagonal microplates: A promising material solution-processed for ultraviolet self-powered photodetectors

In recent times, hybrid organic-inorganic lead halide perovskites have garnered significant attention in the realm of optoelectronic devices. Metal halide perovskites are extensively researched for photodetection due to their exceptional optical and electrical properties. However, the toxicity of lead and the unstable nature of organic components are limiting its potential. Lead-free perovskites, on the other hand, have low toxicity and are being explored as a promising material for photodetector applications. However, achieving self-powered perovskite photodetectors with high photoresponse, broad spectral sensitivity, and long-term stability remains challenging Among them, Cs3Bi2I9 perovskites have emerged as standout, garnering attention for their environmentally friendly nature, impressive stability, and heightened photosensitivity. Herein, FTO/ Al-doped ZnO (AZO)/Cs3Bi2I9/P3HT/C self-powered ultra-violet (UV) photodetector. This device demonstrated outstanding self-powered photodetection capabilities with a photoresponsivity of 29 mA/W, a specific detectivity of 1.05×1011 Jones, and an impressive response rise and decay time of 90 ms /140 ms. Furthermore, the PDs device can function as a bias-based UV photodetector.

A primary wideband calibration method for noise hydrophones based on three-transducer spherical wave reciprocity in the frequency domain.

A primary wideband calibration method for noise hydrophones is developed, which can be applied to obtain noise acoustic spectral density sensitivity in the free-field. In this method, a wideband three-transducer spherical wave reciprocity calibration method is proposed in the frequency domain. A lowpass spatial domain filter is utilized to eliminate the reflecting acoustic waves from boundaries and water surface, and the wideband frequency responses of the transducer pair are calculated. Wideband calibrations are performed in a laboratory anechoic water tank, and two hydrophones with different reference sensitivities are calibrated in the frequency range of 250 Hz to 20 kHz using noise signals. The decidecade band sensitivities are obtained by the primary wideband calibration, which is in agreement with the single frequency sensitivities. The expended uncertainty of the primary wideband calibration is analyzed and estimated to be 8.9% (k = 2).

Deriving the cone fundamentals: a subspace intersection method.

Two ideas, proposed by Thomas Young and James Clerk Maxwell, form the foundations of colour science: (i) three types of retinal receptors encode light under daytime conditions, and (ii) colour matching experiments establish the critical spectral properties of this encoding. Experimental quantification of these ideas is used in international colour standards. However, for many years, the field did not reach consensus on the spectral properties of the biological substrate of colour matching: the spectral sensitivity of the cone fundamentals. By combining auxiliary data (thresholds, inert pigment analyses), complex calculations, and colour matching from genetically analysed dichromats, the human cone fundamentals have now been standardized. Here, we describe a new computational method to estimate the cone fundamentals using only colour matching from the three types of dichromatic observers. We show that it is not necessary to include data from trichromatic observers in the analysis or to know the primary lights used in the matching experiments. Remarkably, it is even possible to estimate the fundamentals by combining data from experiments using different, unknown primaries. We then suggest how the new method may be applied to colour management in modern image systems.

Зависимость величины сигнала от смещения функции рассеяния точки, вписанной в четыре пиксела матрицы

An algorithm has been developed for calculating changes in the signal level of a matrix pixel when the point scattering function is shifted at an angle of 45º relative to the joining point of 4 matrix pixels. In the initial state of the point spread function, the point is inscribed in four pixels. The spectral sensitivity of a pixel is constant within the pixel area. The distribution of pixel irradiance in the point spread function in the form of uniform irradiance is considered. Method. The calculation is based on the method of dividing the point spread function on each pixel of the matrix into separate areas for which the signal is calculated. The displacement of the point scattering function by Δx along the X axis and by Δy along the Y axis is taken in a form normalized to the radius of the spot. To create a two-dimensional graph of the dependence of the pixel signal on the displacement of the point scattering function along the X, Y axes, we introduce the relative displacement of the point scattering function η. Main results. An algorithm has been developed for calculating changes in the signal level of a matrix pixel when the point scattering function is shifted relative to the matrix pixels for the case of pixel irradiation in the lens scattering circle in the form of uniform irradiance. The dependence of the normalized matrix pixel signal on the relative displacement of the point scattering function η at an angle of 45º has been plotted for the above case of irradiation. Practical significance. Matrix photodetectors are widely used in guidance and tracking systems for space objects and astronomical sensors. For a defocused optical system, uniform distribution is used. When the point scattering function shifts relative to the joining point of the four pixels of the matrix, the matrix signal drops, which, with a low signal-to-noise ratio, can lead to a breakdown in tracking or an increase in the error in measuring the angular coordinates of a space object. The results of these studies can be used to model a target guidance system and determine target coordinates.

Slow-wave-enhanced on-chip Michelson interferometer sensor: erratum.

The device described in our earlier paper [Opt. Lett.48, 5968 (2023)10.1364/OL.500033] as a slow wave enhanced on-chip Michelson interferometer sensor is correctly designated as a slow wave enhanced on-chip loop terminated Mach-Zehnder interferometer sensor. In the earlier paper, we experimentally demonstrated slow wave enhanced phase and spectral sensitivity in asymmetric loop-terminated Mach-Zehnder interferometer (LT-MZI) sensors. Compared to Mach-Zehnder interferometers (MZI) that experimentally demonstrated a phase sensitivity 84,000 rad/RIU-cm, the reflected path enhancement of the optical path length coupled with slow light enhancement with photonic crystal waveguides in on-chip slow light loop-terminated Mach-Zehnder interferometer sensors resulted in experimentally demonstrated phase sensitivity 277,750 rad/RIU-cm with theoretical phase sensitivity as high as 461,810 rad/RIU-cm, at the same form factor as the MZI of identical interferometer arm lengths.

Analyzing the Effects of Monochromatic Lights on the Fungal Growth to Control the Progression of Microbial Deterioration on Animal Collections Preserved in the Zoological Museum of Naples, Italy

ABSTRACT Exposing artworks and artifacts in museums is fundamental to disseminate culture and knowledge but is also risky since the exposure to environmental conditions can deteriorate exhibited objects. Light is crucial, being able to trigger photochemical effects, and jointly responsible (with temperature and humidity) for biological risk generation. In this context, fungal growth in museum artifacts is a damaging factor that should not be underestimated. Consequently, the study of lighting effects on fungi development is essential. In this work, five different fungal strains (Aspergillus fumigatus, Bjerkandera adusta, Fusarium oxysporum, Penicillium chrysogenum, and Penicillium granulatum) isolated from samplings on animal exhibits hosted in the Zoological Museum of Naples, Italy, are cultivated inside four experimental boxes, equipped with monochromatic LEDs with different peak wavelengths (460 nm, 518 nm, 594 nm, and 638 nm). The growth rate, the protein and carbohydrate contents are analyzed and compared to results obtained in darkness (typical growth conditions for studies about fungi). Results demonstrate that, even if fungi are heterotrophic organisms and do not need light to grow and develop, their growth rate, and their protein and carbohydrate contents are affected by the exposure to monochromatic radiation, but the spectral sensitivity strictly depends on the analyzed species. For this reason, it is not possible to infer general practical guidelines for lighting applications, and it becomes urgent to establish accurate and shared analysis protocols to be applied case by case, to study the effects of the environmental conditions on microorganisms and drive-specific design choices.

OFS-EFPI ultra-fine manometer based on nitrogen-doped MoS2 diaphragm

Here, an extrinsic Fabry-Pérot interferometer-based optical fiber sensor is introduced to assess its dynamic/static response according to the acoustic/gas pressure performance. This sensor utilizes nitrogen-doped molybdenum disulfide (N-MoS2) and pristine MoS2 diaphragms. The N-MoS2 nanosheets are synthesized using the pulse laser ablation in liquid nitrogen. According to empirical results, the N-MoS2 diaphragm notably enhances the sensitivity of the sensor against the pristine one. Moreover, both diaphragms exhibit a linear relationship between sensor output and acoustic pressure, demonstrating a nearly flat acoustic frequency response ranging 8 Hz-10 kHz. Regarding the pressure measurements, the spectral sensitivity of the N-MoS2 diaphragm is ∼16 % larger than that of pristine. This sensor is capable of measuring the manometric pressures up to 250 mbar with an accuracy of 0.001 mbar.

Cation-substitution-induced high spectral tunability and thermosensitivity in double halide perovskite Cs2InCl5∙H2O

The advancement of non-contact temperature measurement has brought about significant interest due to its rapid response, broad applicability, and minimal thermal inertia. However, challenges such as spectral peak position modulation, sensitivity improvement, and reliable performance enhancement continue to persist in this field. In this study, a double halide perovskite single-crystal Cs2InCl5∙H2O was synthesized, with the introduction of Bi3+ ions modulating the photoluminescence from orange to blue. Meanwhile, the deep-blue emission peaked at 410 nm, boasting a high photoluminescence quantum yield (PLQY) of nearly 46 % under 340 nm excitation. Furthermore, by incorporating varying concentrations of Bi3+ ions, two distinct emission peaks were generated, facilitating effective signal differentiation for temperature detection. Utilizing the thermal quenching responses of these two emission peaks, a temperature-detection methodology based on the fluorescence intensity ratio (FIR) was developed, using donor-acceptor pair emission as detection signals and self-trapped emission as reference signals. The designed Cs2InCl5∙H2O:0.07Bi3+ exhibits a maximum Sa of 0.082 K-1 and Sr of 3.349 %K−1, respectively. The spectral adjustability and high sensitivity achieved through cation-substitution strategy in this study offer a promising pathway for the development of advanced optical thermometry materials with enhanced performance characteristics.

Probing bilin-protein interaction in the protochromic photocycle of cyanobacteriochrome RcaE by site-directed mutagenesis.

Cyanobacteriochromes (CBCRs) are members of the phytochrome superfamily of photosensor proteins that bind a bilin chromophore. CBCRs exhibit substantial diversity in their absorption wavelengths through a variety of bilin-protein interactions. RcaE is the first discovered cyanobacteriochrome as a regulator of chromatic acclimation, where cyanobacteria optimize the absorption wavelength of their photosynthetic antenna. RcaE undergoes a reversible photoconversion between a green-absorbing (Pg) and a red-absorbing (Pr) states, where the bilin chromophore adopts a deprotonated C15-Z,anti and a protonated C15-E,syn structures, respectively. This photocycle is designated as "protochromic photocycle" as the change of the bilin protonation state is responsible for the large absorption shift. With the guidance of recently determined Pg and Pr structures of RcaE, in this study, we investigated bilin-chromophore interaction by site-directed mutagenesis on three key residues referred to as a protochromic triad and also other conserved residues interacting with the bilin. Among the protochromic triad residues, Glu217 and Lys261 are critical for the formation of the Pr state, while Leu249 is critical for the formation of both Pg and Pr states. Substitution in other conserved residues, including Val218, Phe219, and Pro220 in the wind-up helix and Phe252, Phe214, and Leu209 in a part of the bilin-binding pocket, had less substantial effects on the spectral sensitivity in RcaE. These data provide insights into our understanding of the bilin-chromophore interaction in the protochromic photocycle and also its evolution in the CBCRs.

Practical Advice on Measuring and Applying Light for Laboratory Mammals.

Light is recognized as an important component of the environment for laboratory animals. It supports vision, sets the phase of circadian clocks, and drives wide-ranging adjustments in physiological and behavioral state. Manipulating light is meanwhile a key experimental approach in the fields of vision science and chronobiology. Nevertheless, until recently, there has been no consensus on methods for quantifying light as experienced by laboratory animals. Widely adopted practices employ metrics such as illuminance (units = lux) that are designed to quantify light as experienced by human observers. These weight energy across the spectrum according to a spectral sensitivity profile for human vision that is not widely replicated for non-human species. Recently, a Consensus View was published that proposes methods of light measurement and standardization that take account of these species-specific differences in wavelength sensitivity. Here, we draw upon the contents of that consensus to provide simplified advice on light measurement in laboratory mammal experimentation and husbandry and quantitative guidance on what constitutes appropriate lighting for both visual and circadian function.

Field-domain rapid-scan EPR at 240 GHz for studies of protein functional dynamics at room temperature

We present field-domain rapid-scan (RS) electron paramagnetic resonance (EPR) at 8.6T and 240GHz. To enable this technique, we upgraded a home-built EPR spectrometer with an FPGA-enabled digitizer and real-time processing software. The software leverages the Hilbert transform to recover the in-phase (I) and quadrature (Q) channels, and therefore the raw absorptive and dispersive signals, χ′ and χ′′, from their combined magnitude (I2+Q2). Averaging a magnitude is simpler than real-time coherent averaging and has the added benefit of permitting long-timescale signal averaging (up to at least 2.5×106 scans) because it eliminates the effects of source-receiver phase drift. Our rapid-scan (RS) EPR provides a signal-to-noise ratio that is approximately twice that of continuous wave (CW) EPR under the same experimental conditions, after scaling by the square root of acquisition time. We apply our RS EPR as an extension of the recently reported time-resolved Gd-Gd EPR (TiGGER) [Maity et al., 2023], which is able to monitor inter-residue distance changes during the photocycle of a photoresponsive protein through changes in the Gd-Gd dipolar couplings. RS, opposed to CW, returns field-swept spectra as a function of time with 10ms time resolution, and thus, adds a second dimension to the static field transients recorded by TiGGER. We were able to use RS TiGGER to track time-dependent and temperature-dependent kinetics of AsLOV2, a light-activated phototropin domain found in oats. The results presented here combine the benefits of RS EPR with the improved spectral resolution and sensitivity of Gd chelates at high magnetic fields. In the future, field-domain RS EPR at high magnetic fields may enable studies of other real-time kinetic processes with time resolutions that are otherwise difficult to access in the solution state.

Bifacial Photovоltaic Sensor for Insolation Energy Resource Monitoring

Accurate and reliable measurements of the total solar radiation flux make it possible to evaluate the efficiency of using stand-alone photovaltaic systems in various meteorological conditions. These measurements allow more accurately predict in time the energy production volume, accumulator and capacitive storage devices parameters and the payback period. Research purpose was to study the possibility of creating a photoelectric sensor and a method of uninterrupted measurement based on this sensor which allows to measure total solar radiation flux including its direct, diffused and reflected components simultaneously. The photovaltaic sensor with bifacial photosensitivity was manufactured and applied, which is low-inertia comparing to traditional thermoelectric pyranometers, and its spectral sensitivity is quite close to the same parameter of photovoltaic power supply system. It creates the possibility to estimate the insolation level capable to be completely converted into electrical energy without an ineffective heat-generating long-wavelength part of the solar spectrum. A laboratory measuring stand was made to test the sensor's operability. Modeling and experiments’ the sensor parameters were carried out and confirmed its operability. The bifacial photosensitivity sensor allows to control simultaneously direct, diffused and reflected from the earth's surface components of solar radiation, what gives more complete information about the energy potential of the photovoltaic power supply system location.

Accurate Determination of Camera Quantum Efficiency from a Single Image.

Knowledge of spectral sensitivity is important for high-precision comparison of images taken by different cameras and recognition of objects and interpretation of scenes for which color is an important cue. Direct estimation of quantum efficiency curves (QECs) is a complicated and tedious process requiring specialized equipment, and many camera manufacturers do not make spectral characteristics publicly available. This has led to the development of indirect techniques that are unreliable due to being highly sensitive to noise in the input data, and which often require the imposition of additional ad hoc conditions, some of which do not always hold. We demonstrate the reason for the lack of stability in the determination of QECs and propose an approach that guarantees the stability of QEC reconstruction, even in the presence of noise. A device for the realization of this approach is also proposed. The reported results were used as a basis for the granted US patent.

Ultrastructure and Spectral Characteristics of the Compound Eye of Asiophrida xanthospilota (Baly, 1881) (Coleoptera, Chrysomelidae).

In this study, the morphology and ultrastructure of the compound eye of Asi. xanthospilota were examined by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), micro-computed tomography (μCT), and 3D reconstruction. Spectral sensitivity was investigated by electroretinogram (ERG) tests and phototropism experiments. The compound eye of Asi. xanthospilota is of the apposition type, consisting of 611.00 ± 17.53 ommatidia in males and 634.8 0 ± 24.73 ommatidia in females. Each ommatidium is composed of a subplano-convex cornea, an acone consisting of four cone cells, eight retinular cells along with the rhabdom, two primary pigment cells, and about 23 secondary pigment cells. The open type of rhabdom in Asi. xanthospilota consists of six peripheral rhabdomeres contributed by the six peripheral retinular cells (R1~R6) and two distally attached rhabdomeric segments generated solely by R7, while R8 do not contribute to the rhabdom. The orientation of microvilli indicates that Asi. xanthospilota is unlikely to be a polarization-sensitive species. ERG testing showed that both males and females reacted to stimuli from red, yellow, green, blue, and ultraviolet light. Both males and females exhibited strong responses to blue and green light but weak responses to red light. The phototropism experiments showed that both males and females exhibited positive phototaxis to all five lights, with blue light significantly stronger than the others.

Monitoring Harmful Algal Blooms and Water Quality Using Sentinel-3 OLCI Satellite Imagery with Machine Learning

Cyanobacterial harmful algal blooms release toxins and form thick blanket layers on the water surface causing widespread problems, including serious threats to human health, water ecosystem, economics, and recreation. To identify the potential drivers for the bloom, there is a need for extensive observations of the water sources with bloom occurrences. However, the traditional methods for monitoring water sources, such as collection of point ground samples, have proven limited due to spatial and temporal variability of water resources, and the cost associated with collecting samples that accurately represent this variability. These limitations can be addressed through the use of high-frequency satellite data. In this study, we explored the use of Random Forest (RF), which is one of the widely used machine learning architectures, to evaluate the performance of Sentinel-3 OLCI (Ocean and Land Color Imager) images in predicting bloom proxies in the western region of Lake Erie. The sixteen available bands of Sentinel-3 images were used as the predictor variables, while four proxies of the cyanobacterial masses, including Chlorophyll-a, Microcystin, Phycocyanin, and Secchi-depth, were considered as response variables in the RF models, with one RF model per proxy. Each of the proxies comes with a unique set of traits that can help with bloom detection. Among four RF models, the model for Chlorophyll-a performed the best with R2 = 0.55 and RMSE = 20.84 µg/L, while R2 performance for the rest of the other proxies was less than 0.5. This is because Chlorophyll-a is the most dominant and optically active pigment in water, while Phycocyanin, which is a strong indicator of harmful bloom, is present in low concentrations. Additionally, Microcystin, responsible for bloom toxicity, has limited spectral sensitivity, and Secchi-depth could be influenced by various factors besides blooms, such as colored dissolved organic and inorganic matter. On further examining the relationship between the proxies, Microcystin and Secchi-depth were significantly correlated with Chlorophyll-a, which enhances the usefulness of Chlorophyll-a in accurately identifying the presence of algal blooms.

AUTOMATED SYNTHESIS OF FAST LENSES FOR MODERN NIGHT VISION DEVICES

This article is devoted to research of the possibilities of automated design of fast and high-quality multi-lens objectives intended for use in night vision devices with modern image intensifier tubes of generation 4 and 4+, which have photocathodes with a diameter of up to 18 mm. Such image intensifier tubes are characterized by extended spectral sensitivity, high signal-to-noise ratio, and increased resolution. The computer program PODIL, developed earlier for the automated design of arbitrary optical systems, was applied to find out prescription data of fast lenses. For the parametric synthesis of optical systems, the modified evolutionary algorithm implemented in the program was used. The article presents the general methodology and results of automated parametric synthesis of a series of optical systems of objectives with different focal lengths, which contain from 7 to 9 lenses with spherical surfaces. The synthesized lenses provide angular field of view of 10°, 37° and 60° without any vignetting of axial and peripheral beams. The correspondent F numbers are 1.5, 1.33, and 1.4. The working spectral range of the designed lenses is determined by the spectral sensitivity of the photocathodes of the image intensifier tubes. In this research, it covers wavelengths from 0.45 to 0.9 μm. The longitudinal size of the designed optical systems (i.e. the distance from the first optical surface to the photocathode’s plane) is found within the range from 80 to 106 mm. The presented results of aberration analysis confirm the high image quality of the obtained optical systems. In particular, the maximum spatial frequencies of the evaluated polychromatic diffraction modulation transfer functions of the lenses over the entire field in both meridional and sagittal planes exceed 50 mm-1. The maximum values of relative distortion of the lenses are obtained within the range from 1% to 2%.

Photosystems and photoreceptors in cyanobacterial phototaxis and photophobotaxis.

Cyanobacteria move by gliding motility on surfaces toward the light or away from it. It is as yet unclear how the light direction is sensed on the molecular level. Diverse photoreceptor knockout mutants have a stronger response toward the light than the wild type. Either the light direction is sensed by multiple photoreceptors or by photosystems. In a study on photophobotaxis of the filamentous cyanobacterium Phormidium lacuna, broad spectral sensitivity, inhibition by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and a highly sensitive response speaks for photosystems as light direction sensors. Here, it is discussed whether the photosystem theory could hold for phototaxis of other cyanobacteria.

Overcoming confusion noise with hyperspectral imaging from PRIMAger

ABSTRACT The PRobe far-Infrared Mission for Astrophysics (PRIMA) concept aims to perform mapping with spectral coverage and sensitivities inaccessible to previous FIR space telescopes. PRIMA’s imaging instrument, PRIMAger, provides unique hyperspectral imaging simultaneously covering 25–235 µm. We synthesize images representing a deep, 1500 h deg−2 PRIMAger survey, with realistic instrumental and confusion noise. We demonstrate that we can construct catalogues of galaxies with a high purity (>95 per cent) at a source density of 42 k deg−2 using PRIMAger data alone. Using the XID+ deblending tool, we show that we measure fluxes with an accuracy better than 20 per cent to flux levels of 0.16, 0.80, 9.7, and 15 mJy at 47.4, 79.7, 172, and 235 µm, respectively. These are a factor of ∼2 and ∼3 fainter than the classical confusion limits for 72–96 and 126–235 µm, respectively. At $1.5 \le z \le 2$, we detect and accurately measure fluxes in 8–10 of the 10 channels covering 47–235 µm for sources with $2 \lesssim \log ({\rm SFR}) \lesssim 2.5$, a 0.5 dex improvement on what might be expected from the classical confusion limit. Recognizing that PRIMager will operate in a context where high-quality data will be available at other wavelengths, we investigate the benefits of introducing additional prior information. We show that by introducing even weak prior flux information when employing a higher source density catalogue (more than one source per beam), we can obtain accurate fluxes an order of magnitude below the classical confusion limit for 96–235 µm.

Investigation of optical parameters in Ge source SELBOX tunnel FET under visible spectrum

In this work, we have implemented Ge source Selective buried oxide (SELBOX) Tunnel FET for photo sensing applications in the visible range of spectrum for wavelength (λ = 300–700) nm. The various electrical parameters are extracted under dark and illumination states considering the presence and absence of trap charges at the interface of gate oxide and semiconductor. It is seen that at illumination state, the drain current degrades at low gate voltage and presence of traps lead to reduced tunnelling rate. Further, the spectral sensitivity, responsivity, and signal to noise ratio (SNR) are extracted for this TFET based photosensor with variation in λ. Result reveals that spectral sensitivity, responsivity, and signal to noise ratio (SNR) are 20.8, 0.5, and 49.5 dB, respectively, at λ = 300 nm. Further, the presence of trap charges result in degradation of these parameters. Finally, a comparative study of optical parameters with the existing data is highlighted.