Visible Spectral Range Research Articles

Titan Yellow dye sensitized and Ethylenediaminetetraacetate photoreduced photogalvanic system

Photogalvanic cells (PG) are capable of generating solar power with storage, which predominantly dependent on the sensitizer/electrolyte/electrode nature. Therefore, the exploitation of suitable combination of photo-sensitizer/electrode/electrolyte is the key for enhancing the electrical output of these cells. Titan Yellow (a novel dye) has good absorbance in the visible region and good water solubility. These characteristics of this dye have prompted authors to exploit it for further enhancing electrical output of PG cells. Therefore, in present study, the Titan yellow dye photo sensitizer-Ethylenediaminetetraacetate (EDTA) reductant-NaOH alkali medium-Pt/Graphite electrodes photogalvanic system has been exploited. The observed power, current, potential, and efficiency is of the order of 126.4 µW, 2200 µA, 770 mV and 4.34%, respectively. PG performance is observed better in the high pH range (for example, ∼22% enhancement in the power with 0.87% rise in the pH; 37.6 µW power at pH 13.65; 46 µW power at pH 13.77). Spectroscopic study shows that the Titan Yellow is the actual light absorbing material in the electrolyte as other chemical components (reductant EDTA, NaOH, water) of the electrolyte do not show any absorbance in the visible spectral range. A comparison of present results with published results shows both sides, i.e., present results are higher than some reported data, and lower than some other reported data. The use of graphite counter electrode in the present study is the reason behind the present results being higher than some reported data. The heat induced precipitation of dye from the electrolyte in the present study is the reason behind the present results being lower than some reported data. Therefore, controlling the Titan Yellow precipitation at elevated temperature is the challenge for future research. In totality, the present research shows that the Titan yellow dye is not a good sensitizer in the photogalvanics.

GAS SENSOR BASED ON THE SPECTRAL SPR EFFECT WITH COLORIMETRIC REGISTRATION OF RESPONSES

A new variant of the optoelectronic sensor for the detection of gas molecules based on the effect of spectral surface plasmon resonance (SPR) in the chromatic mode with colorimetric registration of the color components of the reflected light is proposed. As an optical sensitive element, a thin silver film was used on the base face of the prism in the Kretschmann geometry, which made it possible to realize a full-fledged SPR effect in the entire visible spectral range from 450 to 700 nm. To measure the optical response, the method of video registration of R, G, B components of reflected light by color webcam was used. The optical scheme of the set-up allowed to simultaneously obtain the full spectrum of plasmon-reflected light without the use of rotating mechanical parts. The sensory effect was a change in the refractive index of the surrounding medium under the action of gases, which directly affected the parameters of the spectral SPR. A laboratory prototype of an optoelectronic sensor device was created, and the effectiveness of the proposed method was evaluated by detection of a number of organic analytes vapors .

Lanthanide‐FRET Molecular Beacons for microRNA Biosensing, Logic Operations, and Physical Unclonable Functions

AbstractTime‐resolved or time‐gated (TG) biosensing and bioimaging with luminescent lanthanide probes and Förster resonance energy transfer (FRET) have significantly advanced bioanalytical chemistry. However, the development of lanthanide‐based molecular beacons (MBs) has been rather limited. Here, we designed DNA stem‐loop MB probes against two different microRNAs (miR‐21 and miR‐27b) using Tb and Eu FRET donors and quenching (BHQ2) and fluorescent (Cy3) FRET acceptors. Limits of detection down to 190 pM and duplexed miR‐21/miR‐27b quantification at low nanomolar concentrations with Tb‐BHQ2 and Eu‐BHQ2 TG‐FRET MBs demonstrated the versatility and high analytical performance of lanthanide‐based MBs. The particular donor‐acceptor distances in the Tb‐Cy3 MB resulted in inverted nucleic acid target concentration‐dependent TG PL intensities in short (e. g., 0 to 40 μs) and long (e. g., 0.1 to 2.1 ms) TG detection windows after pulsed excitation. We showed that this specific feature of our TG‐FRET MBs can be adapted to the design of molecular logic devices (NOR, OR, NAND, AND, XNOR, XOR, IMPLEMENT, and INHIBIT). Moreover, the almost unlimited choice of TG detection windows and the distinct spectral features of Tb and Cy3 over a broad visible spectral range could be exploited to devise biophotonic physical unclonable functions for highly secure authentication and identification. Our study manifests the versatility of lanthanides for advanced biophotonic applications.

Optimization of the Geometrical Design for an All-Dielectric Metasurface Sensor with a High Refractive-Index Response

This study aims to develop a refractive-index sensor operating in the visible region using an all-dielectric metasurface, which was chosen for its advantages of low optical loss and narrow spectral bandwidth, compared to those of conventional metallic metasurfaces. COMSOL software was utilized as a calculation tool to simulate the resonant properties of an all-dielectric metasurface composed of a circular nanohole-structured titanium oxide (TiO2) thin film, with the aim of enhancing the sensitivity of the refractive index for sensing targets. The simulation focused on finding the best geometrical conditions for the all-dielectric metasurface to achieve high sensitivity. Two resonance modes observed in this metasurface were considered: the quasi-bound-state-in-the-continuum (qBIC) mode and the perfect-reflection (PR) mode. The simulated results demonstrated that high sensitivities of 257 nm/RIU at the PR mode and 94 nm/RIU at the qBIC mode in the visible spectral range could be obtained by periodically constructing the metasurface with a unit cell having a lattice constant of 350 nm, a nanohole radius of 160 nm, and a nanohole depth of 250 nm. Furthermore, the study showed that the resonance mode that enabled high sensitivity was the PR mode, with a sensitivity nearly three times larger than that of the qBIC mode and the ability to reach the highest reflectance at the resonance wavelength. The optimized feature had the highest reflectance at a resonant wavelength of 570.19 nm, and although the quality factor was 25.50, these designed parameters were considered sufficient for developing a refractive index biosensor with high sensitivity and optical efficiency when operating in the visible spectral range.

Overview of the MetSpec project - Artificial meteors in ground testing

We provide an overview of the MetSpec project, which aims to connect meteorite ablation laboratory experiments with meteor spectral observations in the atmosphere aiming at the development of a methodology to identify incoming planetary material distribution into the Earth’s atmosphere. We have selected 28 meteorites of different types to represent known planetary material compositions coming from asteroids, Vesta, Mars and the Moon. Some samples have been tested twice which resulted in overall 31 experiments. Three distinct test campaigns were realized in 2020, 2021 and 2022 with the High Enthalpy Flow Diagnostics Group in the Plasma Wind Tunnel PWK1 where they have developed a unique testing scenario. During the last and most elaborated campaign, 16 cameras observed the artificial meteors in the laboratory. Besides videos and online live streaming, instruments included several spectrometers, and optical and imaging instruments covering UV, visible and IR spectral range. This special collection in Icarus collects the resulting output from the different instruments and results. This overview article provides an introduction and summarizes the main findings of the experimental campaigns.

Synthesis of the Diamond‒SiO2 Composites with the Properties of Photonic Crystals in the Visible Spectral Range

Synthesis of the Diamond‒SiO2 Composites with the Properties of Photonic Crystals in the Visible Spectral Range

Electronic and optical properties of boron-containing GaN alloys: The role of boron atom clustering

Boron (B) containing III-nitride materials, such as wurtzite (wz) (B, Ga)N alloys, have recently attracted significant interest due to their ability to tailor the electronic and optical properties of optoelectronic devices operating in the visible and ultraviolet spectral range. However, the growth of high quality samples is challenging and B atom clustering is often observed in (B, Ga)N alloys. To date, a fundamental understanding of the impact of such clustering on the electronic and optical properties of these alloys is sparse. In this work, we employ density functional theory (DFT) in the framework of the meta-generalized gradient approximation [modified Becke Johnson (mBJ) functional] to provide insight into this question. We use mBJ DFT calculations, benchmarked against state-of-the-art hybrid functional DFT, on (B, Ga)N alloys in the experimentally relevant B content range of up to 7.4%. Our results reveal that B atom clustering can lead to a strong reduction in the bandgap of such an alloy, in contrast to alloy configurations where B atoms are not forming clusters, thus not sharing nitrogen (N) atoms. We find that the reduction in bandgap is linked mainly to carrier localization effects in the valence band, which stem from local strain and polarization field effects. However, our study also reveals that the alloy microstructure of a B atom cluster plays an important role: B atom chains along the wz c axis impact the electronic structure far less strongly when compared to a chain formed within the c-plane. This effect is again linked to local polarization field effects and the orbital character of the involved valence states in wz BN and GaN. Overall, our calculations show that controlling the alloy microstructure of (B, Ga)N alloys is of central importance when it comes to utilizing these systems in future optoelectronic devices with improved efficiencies.

Periodic liquid crystalline waveguiding microstructures

Different methods allowing for creating optical waveguides with liquid–crystal (LC) cores, in which molecules form periodic patterns with precisely controlled periods, are reported. The first one is based on reversible photoalignment with high-resolution selective illumination and allows to control the period of LC molecules inside silica microcapillaries. The second method employs microstructures formed in PDMS, allowing to obtain both: LC-core waveguides and a set of specially designed periodic microelectrodes used for the periodic reorientation of molecules. Using both methods, we successfully controlled the period of the patterned alignment in the range from about 500 µm and scaled it down to as small as 20 µm. We performed experimental studies on waveguiding phenomenon in such structures, in view to obtain transmission spectra typical to optical fiber gratings. Since the results achieved in experimental conditions differed from those expected, the additional numerical simulations were performed to explain the observed effects. Finally, we obtained the waveguiding in a blue phase LC, characterized by naturally created three-dimensional periodicity with periods smaller than one micrometer. In such a structure, we were able to observe first-order bandgap, and moreover, we were able to tune it thermally in nearly the whole visible spectral range.

Fabrication of 2D+1D nanoarchitecture for transition metal oxide modified CdS nanorods: A comparative study on their photocatalytic hydrogen-generation efficiency

We report the formation of Mo1−xWxO3-CdS (0 ≤ x ≤1) nanophotocatalysts by a combination of solid-state and solution-impregnation processes. The formation of 2D+1D heterostructured composite was revealed by electron microscopy and the structure of ternary co-catalyst and photocatalysts were confirmed by spectroscopic analyses. The H2 evolution activity of the nanocomposites was assessed via photocatalytic splitting of water under the irradiation of visible light. All the nanocomposites studied here exhibit notable catalytic activity and good photostability using lactic acid as the sacrificial electron donor compared to a pristine compound. Among these nanocomposites, WO3-CdS shows superior activity with H2 evolution rates of 15.19 mmolg−1h−1, 28 times higher than the pure CdS. The WO3-CdS photoactivity is not only superior among all the composites studied here but also highest among the reported WO3 composite catalysts to date. The novel construction of the oxide-based nanocomposite photocatalyst shown here efficiently enhances the catalytic activity by effective separation of charge carriers and inhibits photocorrosion of CdS nanorods. The apparent quantum yield of the hydrogen evolution for WO3-CdS was found to be 8% in the visible spectral range. The disparity of the catalytic ability between MoO3 and WO3 and the variance among the compositions was unraveled through optical band-offset alignment with respect to CdS. Though the 2D+1D novel fabrication is common to all the composites, the difference in the type of band alignment MoO3 (type-I) and WO3 (type-II) with CdS plays a highly significant role in the co-catalytic activity.

Combined Structural and Plasmonic Enhancement of Nanometer-Thin Film Photocatalysis for Solar-Driven Wastewater Treatment.

Titanium dioxide (TiO2) thin films are commonly used as photocatalytic materials. Here, we enhance the photocatalytic activity of devices based on titanium dioxide (TiO2) by combining nanostructured glass substrates with metallic plasmonic nanostructures. We achieve a three-fold increase of the catalyst's surface area through nanoscale, three-dimensional patterning of periodic, conical grids, which creates a broadband optical absorber. The addition of aluminum and gold activates the structures plasmonically and increases the optical absorption in the TiO2 films to above 70% in the visible and NIR spectral range. We demonstrate the resulting enhancement of the photocatalytic activity with organic dye degradation tests under different light sources. Furthermore, the pharmaceutical drug Carbamazepine, a common water pollutant, is reduced in the aqueous solution by up to 48% in 360 min. Our approach is scalable and potentially enables future solar-driven wastewater treatment.

Growth of SrMoO3 thin films by suboxide molecular beam epitaxy

Among ABO3 perovskites, SrMoO3 possesses the lowest electrical resistivity in addition to having high optical transparency in the visible spectrum. This unusual combination of material properties allows it to be a potential replacement for indium tin oxide as a transparent electrode. Thus far, its thin film synthesis has been challenging and limited primarily to pulsed laser deposition and sputtering. Here, we report the growth of SrMoO3 thin films by suboxide molecular beam epitaxy. We demonstrate that optically transparent and conductive SrMoO3 films can be grown by supplying elemental strontium via a conventional effusion cell and thermally evaporating MoO3 pellets as a molybdenum source. The direct supply of a molecular oxygen flux to the MoO3 charge was utilized to prevent reduction to lower oxidation states of the charge to ensure congruent evaporation and, thus, a stable MoO3 molecular flux. The optimal growth conditions were found by varying the Sr to MoO3 flux ratio determined from quartz crystal microbalance measurements and monitoring the growth by reflection high-energy electron diffraction. SrMoO3 thin films with 21 nm thickness were confirmed to be optically transparent with transmission between 75 and 91% throughout the visible spectral range and electrically conducting with a room temperature resistivity of 5.0 × 10−5 Ω cm. This realization of this thin film growth method can be further expanded to the growth of other transition metal perovskites in which cations have extremely low vapor pressure and cannot be evaporated in elemental forms.

Porous Ceramic ZnO Nanopowders: Features of Photoluminescence, Adsorption and Photocatalytic Properties

The grainy and porous ZnO powders were synthesized by thermal decomposition of zinc nitrate and polymer-salt method. The comparative study of the crystal structure, morphology, luminescence, adsorptive and photocatalytic properties of ZnO powders was carried out. The addition of PVP in initial aqueous solutions of zinc nitrate determines the remarkable change of powder morphology and decreases the average size of ZnO nanocrystals. Luminescence spectra in the visible spectral range indicate the significant difference of structural defects types in grainy and porous powders. Porous powders demonstrate high ability for singlet oxygen photogeneration and photocatalytic properties. The kinetics of diazo dye adsorption on both powders is described successfully by the kinetic equation of pseudo-second order. Kinetic dependencies of photocatalytic oxidation of Chicago Sky Blue diazo dye using as grain ZnO powder so as porous ZnO powders are described by the Langmuir–Hinshelwood model but process rates are different. Porous ZnO powder demonstrates strong ability for photogeneration of singlet oxygen under visible irradiation and high photocatalytic properties (rate constant 0.042 min−1).

Development of primary reference facilities and measurement comparison of standard artifacts for the bidirectional transmittance distribution function

To determine the bidirectional transmittance distribution function (BTDF) of diffusely transmitting materials, two new primary facilities have been developed at the Physikalisch-Technische Bundesanstalt (PTB) and Aalto University (Aalto). A detailed description of both facilities and the different approaches used are presented in this paper. The performance of both facilities is compared by determining the BTDF of two different diffuser types in both in-plane and out-of-plane bidirectional geometries at four different wavelengths in the visible spectral range. Due to delayed completion of PTB’s primary facility, the measured BTDF values are compared between Aalto’s primary facility and another PTB setup, whose measurement scales are successfully transferred to PTB’s primary facility by an internal comparison. A thorough analysis of the measurement uncertainty is presented, leading to a combined k = 1 standard uncertainty of 0.8%–1.2% for PTB’s primary facility and 1.3%–1.7% for Aalto’s primary facility. The BTDF results obtained agree well within their expanded k = 2 uncertainty. This indirect bilateral comparison shows that Aalto’s and PTB’s new facilities are suited as primary reference setups for the determination of the BTDF. These studies also reveal action points to improved measurement capabilities and for a reduction of the measurement uncertainty, depending on the type of diffuser under test.

Enabling infinite Q factors in absorbing optical systems

Abstract Resonant optical structures have widespread applications in science and technology. However, their quality (Q) factors can be significantly deteriorated, if some of their parts exhibit optical absorption. Here, we show that by coupling a lossy mode of such a structure to two independent lossless modes, one can create a nonradiating and absorption-free bound state in the continuum (BIC). The Q factor of such a BIC is theoretically unlimited despite interaction with an absorbing structure. We use this mechanism to design a plasmonic metasurface with Q factors that are close to 107 in the visible spectral range. The proposed mechanism is general and can be used to engineer ultrahigh-Q resonances in various systems containing absorbing structures.

Supersymmetry Laser Arrays with High‐Order Exceptional Point

Supersymmetry (SUSY) laser array with superpartner structure can suppress excess modes to achieve high‐intensity and high‐coherent radiation. Compared with complex superpartner, using parity time (PT) symmetry broken to manipulate SUSY laser arrays is a more flexible approach. Herein, based on ultrathin perovskite single crystal, a SUSY laser array is constructed without superpartner, but with auxiliary gain–loss structure. PT symmetry broken with high‐order exceptional point (EP) is realized in the visible spectral range. It intrinsically avoids superpartner field mismatch and improves side mode suppression ratio 8.8–12 dB for single‐mode lasing. Furthermore, variations in EP‐order enable the transition from single‐mode to dual‐mode or tri‐mode radiation and retain amplified radiation characteristics. In addition, these SUSY laser arrays with the high‐order EP have the potential to be small‐volume optical sensor devices. The new design combining SUSY and PT symmetry broken presents its potential in micro‐nanophotonic devices with the benefit of small size, flexibility in spectral control, expandability, simplicity, and multifunctionality feature.

Nonlinear optical effects in natural topaz

We investigate the nonlinear optical properties of natural topaz. For the first time, the observation of nonlinear phenomena related to multiphoton absorption effects, such as the up-conversion luminescence of the material defects, is reported in natural gems. In particular, we were able to detect the presence of the AlO4-related defects which are responsible for the change of the color of topaz as a consequence of irradiation with γ-rays as well as electrons and neutrons beams. Besides, the nonlinear spectral broadening of intense laser beams permits to spot of the presence of rare earth elements, such as Ytterbium and Neodymium, which are not found by means of standard characterization techniques of natural gems, e.g., those based on X-ray fluorescence, electron paramagnetic resonance, and linear optical fluorescence and absorbance measurements. In this sense, our results demonstrate that nonlinear optical effects induced luminescence measurements are a complementary, and previously unforeseen, technique for the characterization of the optical and physicochemical properties of natural gems. Finally, using intense infrared laser pulses allowed us to trigger extreme nonlinear effects, such as multiphoton ionization and conical emission. Our results will be of interest for the investigation of novel nonlinear optical effects in materials that are transparent in the whole visible spectral range and may give insights into the development of materials for nonlinear photonics.

A 16-year global climate data record of total column water vapour generated from OMI observations in the visible blue spectral range

Abstract. We present a long-term data set of 1∘×1∘ monthly mean total column water vapour (TCWV) based on global measurements of the Ozone Monitoring Instrument (OMI) covering the time range from January 2005 to December 2020. In comparison to the retrieval algorithm of Borger et al. (2020), several modifications and filters have been applied accounting for instrumental issues (such as OMI's “row anomaly”) or the inferior quality of solar reference spectra. For instance, to overcome issues related to low-quality reference spectra, the daily solar irradiance spectrum is replaced by an annually varying mean earthshine radiance obtained in December over Antarctica. For the TCWV data set, we only consider measurements with an effective cloud fraction less than 20 %, an air mass factor (AMF) greater than 0.1, a snow- and ice-free ground pixel, and an OMI row that is not affected by the row anomaly over the complete time range of the data set. The individual TCWV measurements are then gridded to a regular 1∘×1∘ lattice, from which the monthly means are calculated. The investigation of sampling errors in the OMI TCWV data set shows that these are dominated by the clear-sky bias and cause on average deviations of around −10 %, which is consistent with the findings of previous studies. However, the spatiotemporal sampling errors and those due to the row-anomaly filter are negligible. In a comprehensive intercomparison study, we demonstrate that the OMI TCWV data set is in good agreement with the global reference data sets of ERA5 (fifth-generation ECMWF atmospheric reanalysis), RSS SSM/I (Remote Sensing Systems Special Sensor Microwave Imager), and CM SAF/CCI TCWV-global (COMBI): over ocean the orthogonal distance regressions indicate slopes close to unity with very small offsets and high coefficients of determination of around 0.96. However, over land, distinctive positive deviations of more than +10 kg m−2 are obtained for high TCWV values. These overestimations are mainly due to extreme overestimations of high TCWV values in the tropics, likely caused by uncertainties in the retrieval input data (surface albedo, cloud information) due to frequent cloud contamination in these regions. Similar results are found from intercomparisons with in situ radiosonde measurements from version 2 of the Integrated Global Radiosonde Archive (IGRA2) data set. Nevertheless, for TCWV values smaller than 25 kg m−2, the OMI TCWV data set shows very good agreement with the global reference data sets. Furthermore, a temporal stability analysis proves that the OMI TCWV data set is consistent with the temporal changes in the reference data sets and shows no significant deviation trends. As the TCWV retrieval can be easily applied to further satellite missions, additional TCWV data sets can be created from past missions, such as the Global Ozone Monitoring Experiment-1 (GOME-1) or the SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY); under consideration of systematic differences (e.g. due to different observation times), these data sets can be combined with the OMI TCWV data set in order to create a data record that would cover a time span from 1995 to the present. Moreover, the TCWV retrieval will also work for all missions dedicated to NO2 in the future, such as Sentinel-5 on MetOp-SG. The Max Planck Institute for Chemistry (MPIC) OMI total column water vapour (TCWV) climate data record (CDR) is available at https://doi.org/10.5281/zenodo.7973889 (Borger et al., 2023).

Features of the joint use of visible-range satellite and satellite radar data for monitoring arctic icebergs based on data from Franz Josef Land area

Given the availability of data, in order to monitor icebergs in the vast Arctic region, it is necessary to ensure an optimal ratio of the satellite radar data cost (with a wide swath and high spatial resolution) and the reliability of the results obtained. The aim of the study was to evaluate the effectiveness of using only non-commercial satellite information for monitoring icebergs. To achieve this goal, an iceberg detection technique was applied based on statistical criteria of searching for gradient zones in analyzing two-dimensional fields of satellite images. As a source of information, we used high spatial resolution satellite data obtained from non – commercial satellites Sentinel-1 (radar data) and Landsat-8 (visible spectral range data) with a pixel size of 40 × 20 and 15 m, respectively.Through comparison with the data of the visible spectral range of ultra-high resolution, the error was estimated of measuring the size of icebergs using the visible range equipment of the Landsat-8 satellite and the radar of the Sentinel-1 satellite. Based on the analysis of satellite data of the visible spectral range and radar data, the spatial dimensions of icebergs formed by the outlet glaciers of Franz Josef Land n 2020–2022 were estimated. The materials were collected for the period August-September, corresponding to the conditions of minimum ice extent in the Franz Josef Land area and sufficient natural illumination for using the data of the visible spectral range in the Arctic. In total, about 100 satellite images were analyzed. The sources of error in the satellite measurements are discussed, as well as the reasons for the impossibility in some cases to identify Franz Josef Land icebergs on radar images. It is shown that the largest contribution to the iceberg runoff of Franz Josef Land is made by outflow glaciers located on Georg Land, Wilczek Land, Gall, Salisbury and Champa islands. According to the results of the study, it is concluded that radar data with a pixel size of 40 m allow one to obtain essentially reliable information on the spatial distribution of icebergs in the water area. However, it is not possible to obtain a reliable function of the distribution of icebergs by size since most of the icebergs in the Franz Josef Land water area have small and medium sizes and are rarely identified in images of such spatial resolution.

A Candidate Dual QSO at Cosmic Noon

We report the discovery of a candidate dual QSO at z = 1.889, a redshift that is in the era known as “cosmic noon” where most of the universe’s black hole and stellar mass growth occurred. The source was identified in Hubble Space Telescope WFC3/IR images of a dust-reddened QSO that showed two closely separated point sources at a projected distance of 0.″26, or 2.2 kpc. This red QSO was targeted for imaging to explore whether red QSOs are hosted by merging galaxies. We subsequently obtained a spatially resolved Space Telescope Imaging Spectrograph spectrum of the system, covering the visible spectral range, and verifying the presence of two distinct QSO components. We also obtained high-resolution radio continuum observations with the Very Long Baseline Array at 1.4 GHz (21 cm L band) and found two sources coincident with the optical positions. The sources have similar black hole masses, bolometric luminosities, and radio-loudness parameters. However, their colors and reddenings differ significantly. The redder QSO has a higher Eddington ratio, consistent with previous findings. We consider the possibility of gravitational lensing and find that it would require extreme and unlikely conditions. If confirmed as a bona fide dual QSO, this system would link dust reddening to galaxy and supermassive black hole mergers, opening up a new population in which to search for samples of dual active galactic nuclei.

ASPHERIC TWO-MIRROR TELESCOPES OF NANOSATELLITES FOR REMOTE EARTH SENSING AND SEARCH OF MINERALS

The optical system is one of the important components of any space satellite used to observe the Earth's surface or astronomical objects. Due to the small overall size of nanosatellites, lens objectives with the relatively short focal length are often used. The latter provides the sufficiently wide field of view, but limits the spatial resolution of obtained images. In addition, to address various problems in agriculture and geodesy, it is important to obtain images of the earth's surface in different spectral ranges. This fact prevents the application of widespread commercial photographic lenses corrected for the visible spectral range. The article presents the results of the automated parametric synthesis of centered and decentered aspheric optical systems of mirror telescopes based on the Ritchie-Chretien scheme. The obtained optical systems have the focal length of 547 mm, the square entrance aperture of 80×80 mm, and the axial length that does not exceed the size of two CubeSat units. The angular field of view of the telescopes, which is equal to 0.7° in diagonal, enables to apply modern matrix image sensors having a diagonal of the sensitive area up to 6.7 mm. For an axial beam, 90% of the radiation energy falls into a square area of the image with a side of 2.5 μm. The maximum value of relative distortion does not exceed 0.4 %. The considered mirror systems do not have chromatic aberrations, which makes it possible to obtain high-quality images not only in the visible spectral range, but also in several infrared sub-bands. The given results of the aberration analysis testify to the high image quality achieved in both variants. The presented optical systems can observe a rectangular area of the Earth's surface with the diagonal size of about 7.9 km from the satellite’s track height of 650 km. When using a multi-element image detectors with the pixel size of 3 μm, the geometric projection of one pixel on the Earth's surface will be equal to 3.6 m.