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Periodic gratings with complex shapes are designed by machine learning as emitters for a thermophotovoltaic system with a GaSb photovoltaic absorber operating at 1000K in order to maximize thermophotovoltaic efficiency. We also demonstrate complex-shaped GaN grating VCSEL mirrors designed by machine learning for high reflectivity and a wide stopband with center wavelength of 500nm. The results obtained indicate a 50% increase in stopbandwidth for the complex-shaped grating over that of a rectangular grating.

Ga2O3 micro- and nanowires-based optical microcavities have been obtained by patterning pairs of distributed Bragg reflectors (DBRs) with a focused ion beam (FIB) microscope. DBRs result in widely tunable high reflectivity bands. The microcavities have been designed and optimized with the aid of simulations and optically characterized by micro-photoluminescence. Tunable strong modulations are confirmed in the NUV-blue as well as in the red-NIR ranges for unintentionally doped and chromium doped wires, respectively. Experimental, analytical and simulations results will be compared and some possible applications of these cavities will be assessed.

We demonstrate a theoretical approach whereby light backscattering toward the incident beam can be suppressed entirely for a high-reflectivity, rough-surfaced multilayer mirror fabricated using oblique deposition, such that the interface relief is replicated at a certain angle β to the sample normal. The mirror comprises two parts: a main (lower) multilayer consisting of N identical bi-layers growing at the angle βML to the mirror normal, and an additional bi- or tri-layer forming the topmost section of the mirror, which grows at another angle βBL. We show that choosing appropriate growth angles βML and βBL results in a disappearance of backscattering toward the incident beam due to the destructive interference of waves scattered from the main multilayer and uppermost bi- or tri-layer. The conditions for the scattering suppression are formulated, and the suitability of different mirror materials is discussed.

Many experiments in modern quantum optics require the implementation of lightweight and near-perfect reflectors for noise reduction and high sensitivity. Another important application of low mass and high reflectivity mirrors is related to the development of solar or laser-driven light sails for acceleration of ultra-light spacecrafts to relativistic velocities. Here, we present numerical results and theoretical analysis of a metasurface mirror consisting of periodically arranged silicon nanospheres embedded in a polymer. In the absence of material losses or disorder, this mirror demonstrates absolute 100% reflection at a single wavelength, which can be tuned by changing nanosphere dimensions or periodicity (for example, by mechanical stretching). We show that high reflectivity can be reached due to electric or magnetic dipole resonant responses of Si nanoparticles in the metasurface. Dependence of mirror reflectivity on surrounding conditions, nanoparticle sizes, and the disorder in the array is studied and discussed. The optimization and simulation procedures presented in this work can be used for the development of other optical devices with functional characteristics determined by the resonant interaction of light with metasurfaces made of nanospheres. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.

The deep blue (DB) algorithm is usually used for retrieval of AOD on high reflectivity surfaces, which cover complex surface types. However, due to low spatial resolutions, it shows limited information details in urban areas and cannot fully display the aerosol variation characteristics. Now, a new aerosol retrieval algorithm with a priori Land Surface Reflectance (LSR) database support (HARLS) is proposed for Landsat-8 (OLI) images at 1km spatial resolution to use the look-up table (LUT) method to retrieve AOD. The continental aerosol type defined in the 6S model is modified by AERONET single scattering albedo (SSA) parameter to correct the LUT for different seasons, and deep learning neural network is used to train the samples based on the corrected LUT and retrieve AOD. The retrieved AOD are then validated against the aerosol robotic network (AERONET) AOD ground measurements from five stations in Beijing and compared with MOD04 C6.1 10km AOD product. The overall results demonstrate that the AOD retrieved is highly consistent with the AOD derived from ground measurements.

Low-cost all-metal partially reflecting surface (AM PRS) based resonant-cavity antennas are presented in this paper. The AM PRSs are made by introducing square-shaped slots in a thin metallic sheet having moderate to high reflectivity ranging from -4.12 dB to -1.27 dB. An RCA designed using highly reflecting AM PRS has maximum directivity of 16.54 dBi and low 3 dB directivity bandwidth of 9.17% whereas those designed using less reflective AM PRSs have high directivity bandwidth but smaller peak directivity within the operating band.

We demonstrate a hybrid phononic/photonic crystal mirror for optomechanics. A localized mechanical mode is created by a defect in a phononic crystal, which in turn supports a photonic crystal designed for high reflectivity.

The advent of optical metasurfaces, i.e. carefully designed two-dimensional nanostructures, allows unique control of electromagnetic waves. To unlock the full potential of optical metasurfaces to match even complex optical functionalities, machine learning provides elegant solutions. However, these methods struggle to meet the tight requirements when it comes to metasurface devices for the optical performance, as it is the case, for instance, in applications for high-precision optical metrology. Here, we utilize a tandem neural network framework to render a focusing metamirror with high mean and maximum reflectivity of Rmean = 99.993 % and Rmax = 99.9998 %, respectively, and a minimal phase mismatch of Δϕ = 0.016 % that is comparable to state-of-art dielectric mirrors.

Landmines represent a serious environmental problem for several countries as it causes severe injured and many victims. In this paper, the response of GPR from different parameters of the landmine targets has been shown and the data is correlated with observed field experiment made in 2012 at Miami Crandon Park test site. The ability of GPR for detecting non-metallic mines with different orientations was revealed and soil effect upon the GPR signal was examined putting into consideration the soil parameters in different locations in Egypt such as in Sinai and El Alamein. The simulation results showed that PMN-2 landmine was detected at 5 cm and 15 cm depths, even at the minimum radar cross section vertical orientation. The B-Scan (2D GPR profiles) of PMN-2 target at 15 cm depth figured out high reflectivity for Wadi deposits due to large contrast between PMN-2 landmine material and soil of sand dunes. Keywords: GPR, Non-metallic landmines, Orientation angle, Soil parameters and field experiment and simulation

Here, we propose, fabricate and characterize the light manipulation of a suspended-membrane InGaN/GaN multiple-quantum-well light-emitting diode (MQW-LED) with a dielectric distributed Bragg reflector (DBR) positioned at the bottom, implemented on a GaN-on-silicon platform. Silicon removal is conducted to obtain the suspended MQW-LED architecture, and back wafer thinning of the epitaxial film is performed to improve the device performance. A 6-pair SiO2/Ta2O5 DBR is deposited on the backside to manipulate the emitted light. The experimental results demonstrate that the bottom dielectric DBR exhibits high reflectivity and distinctly changes the light emission, which are consistent with the performed simulation results. This work represents a significant step towards the realization of inexpensive, electrically driven and simply fabricated GaN VCSELs for potential use in number of applications.

Highly reflective metal contacts for the p-layers of AlGaN-based deep ultraviolet light emitting diodes (DUV LEDs) emitting at 305 nm have been investigated. Different Pd-Al metal stacks have been examined and a reflectivity of 82% was obtained after annealing, which is about two times the value measured for conventional Pd contacts. The high reflectivity is attributed to the formation of an Al4Pd phase besides an Al phase in the annealed contact. DUV LEDs with highly-reflective Pd-Al contacts exhibited an increase of the light output power by 30% at a dc current of 20 mA.

We observe a shadow image when a Lidar based on a MEMS mirror scans targets located on the surface of high reflectivity. Furthermore, the shadow seriously deteriorates the ability of the Lidar to distinguish characteristics (i.e. distance, shape, etc.) of the targets. We prove that the high reflectivity floor is the key of the shadow formation at first, then study the differences of the light path and the laser energy between the normal and shadow image. Based on these differences, we study the possibility of eliminating the shadow. Finally, we take the methods of flipping and direct-pass filtering to eliminate the shadow. High reflectivity surface is inevitable in the Lidar application environment, especially when the Lidar is used in the automation vehicles, so removing the shadow is significant for the popularization of the Lidar in auto-driving machines.

The aim of this research is to investigate the possibility of applying a laser distance meter (LDM) as a complementary measurement method to image analysis during beer foam stability monitoring. The basic optical property of foam, i.e., its high reflectivity, is the main reason for using LDM. LDM measurements provide relatively precise information on foam height, even in the presence of lacing, and provide information as to when foam is no longer visible on the surface of the beer. Sixteen different commercially available lager beers were subjected to analysis. A camera and LDM display recorded the foam behavior, the LDM display which was placed close to the monitored beer glass. Measurements obtained by the image analysis of videos provided by the visual camera were comparable to those obtained independently by LDM. However, due to lacing, image analysis could not accurately detect foam disappearance. On the other hand, LDM measurements accurately detected the moment of foam disappearance since the measurements would have significantly higher values due to multiple reflections in the glass.

A novel uni-traveling-carrier photodetector (UTC-PD), bonded to high-reflectivity (HR) distributed Bragg reflector (DBR) mirrors, referred to as HR-UTC-PD, is first developed to overcome the bandwidth-responsivity tradeoff in UTC-PDs at various wavelengths. Grubbs' test is adopted, for the first time, to measure the bonded thickness of random locations for evaluating the reflected light loss generated in the bonded region. Compared with a standard UTC-PD without HR DBR mirrors, the maximum improvement of HR-UTC-PD responsivity (0.88A/W at 1560 nm) is 24.4% under a bias voltage of 3 V. The obtained 3-dB bandwidth for a 40-μm-diameter PD, which is neither increased nor degraded with the HR DBR mirrors, is 13.87 GHz at a bias voltage of 6 V and a 1550 nm wavelength. The saturation current up to 50 mA at 1-dB compression point is obtained at the frequency of 10 GHz, under a 50-Ω load and a 6 V bias voltage.

Much interest has been paid to omnidirectional dielectric mirrors based on the 1-D dielectric multilayers because these are better than metal mirrors owing to their low optical loss, high reflectivity and high mechanical robustness. In these applications, the required position and width of the reflection band can be obtained by adjusting the layer thickness and refractive indices of the constituent materials. Here, the omnidirectional reflection characteristics of a 1-D PC formed by TiO2/SiO2 multi-quantum wells (MQW) are investigated in the visible region. It is demonstrated that the omnidirectional high reflector, formed by the proper line-up of four TiO2/SiO2 MQWs, covers the visible band approximately when the number of periodic layers of each quantum well reaches 12. This study can provide guidance in the design of an omnidirectional high reflector in the visible band. Key words: Omnidirectional reflector, photonic crystals, multi-quantum wells.

Radiant slab systems have the potential to achieve significant energy savings, yet, when applied in the ceiling (e.g., thermally activated building system) the exposed concrete may also create acoustical challenges due to the high reflectivity of the hard surface. Balancing all of the building indoor environmental quality factors is important in the design of an effective workspace for the occupants, and so we need to consider the interactions between thermal and acoustic comfort. We assessed the cooling capacity in a hydronic test chamber and the sound absorption in a reverberation chamber to study the effects, for an office room, of different coverage areas of free-hanging acoustical clouds below a radiant chilled ceiling. The cooling experiments showed that for 47% cloud coverage of the ceiling area, we measured only an 11% reduction in cooling capacity caused by the blockage of radiant exchange between the ceiling and the room. The acoustical results showed that if the cloud covered 30% of the ceiling in a private office or 50% in an open plan office, acceptable sound absorption at the ceiling was achieved. We showed that good acoustic quality can be achieved with only a minor reduction of cooling capacity.

Dye-doped nematic liquid crystal refilled gradient-pitched enantiomorphic cholesteric liquid crystal polymer templates are demonstrated. The enantiomorphic device has high reflectivity and wide spectral tunability throughout the entire visible region. This device can also provide low threshold lasing emission with both right- and left-circular polarizations from the blue to the red region.

The sensitivity and visual acuity of the eye of the shrimp L. vannamei are achieved via an exquisitely optimized nanostructured tapetum leading to a very high reflectivity in an ultrathin layer. Understanding the properties of such natural nanostructures can lead to the design of artificial photonic materials with enhanced properties.

Smart utilization of solar energy with OVW (Optic-Variable Wall) for thermal comfort is verified. The application of OVW in passive buildings is discussed. With no active heating & cooling measure adopted for building located in Shanghai, OVW can offer relatively comfortable environment in the whole year period. Compared with reflective OFW (Optic-Fixed Wall with high reflectivity), the cold period in winter is shortened and meanwhile the summer is kept cool. Compared with absorptive OFW (Optic-Fixed Wall with low reflectivity), the hot period in summer is enormously suppressed and the winter is kept warm. The performance of thermal comfort, e.g. Discomfort Hours, Discomfort-Degree Hours and Discomfort Degree, is significantly improved. Comparing with OFW, both reflective and absorptive, less discomfort hours and less discomfort-degree hours are concluded with the adoption of OVW. The average discomfort-degree of OVW is the least in summer as well as in winter, although the average discomfort-degree in the whole-year period is slightly larger than absorptive OFW. It is also concluded that absorptive OFW performs better than reflective OFW on Discomfort-Degree Hours, but worse on Discomfort Hours. The results are also meaningful for other applications, such as vehicles and light-steel-structured industrial warehouse.

Situated in Central Europe, the Milesovka observatory was equipped with a vertically oriented Ka-band cloud radar (35 GHz) in spring 2018. We analysed strong convective events that were observed in summer 2018 at the observatory and were detected by the cloud radar, which read high reflectivity values. We applied our algorithm treating the radar data to retrieve vertical air velocity and five types of hydrometeors and we conducted a comparative study of the results with ground-based measurements of lightning. The study showed that hail and rain are the two hydrometeors, which clearly tend to be more frequent in convective clouds that are situated above the cloud radar, when a lightning is recorded in the vicinity of the Milesovka observatory. Similarly, in case of nearby lightning downdrafts are observed at lower altitudes (up to 4 km above the radar), whereas slight updrafts are more typical for higher altitudes above the radar.

Due to the high reflectivity of the resistor array in the target scene generator (TSG), the narcissus effect caused by the resistor array is notorious. Based on the paraxial analysis of the resistor array, the telecentric structure in the image space is proposed to reduce the narcissus effect induced by the resistor array. A TSG with the telecentric structure in the image space and a TSG with the nontelecentric structure in the image space, which have same system parameters, are designed and optimized. The nonsequential ray tracing technique is used for both TSGs to evaluate the narcissus effect induced by the resistor array. The simulation results show that using a telecentric structure in the imaging space is an effective method to suppress the narcissus signal caused by the resistor array.

A simulation is made of the propagation of a thermo-optical traveling wave along a silicon wafer surface containing an isolated optical inhomogeneity which critically changes a balance of input and output heat in the position of the localization of the wave. The optical inhomogeneity is represented by a strip of sputter-coated material with high reflectivity which is applied on the wafer and whose reflectivity and width are varied in the simulation process. Depending on these parameters, the traveling wave either delays its propagation passing through the optical inhomogeneity or stops at a boundary of the strip. It has been shown that a critical width of the strip at which a thermooptical traveling wave is localized increases as strip reflectivity decreases.

The effect of gamma radiation on the optical loss of high reflectivity monocrystalline supermirrors will be presented. These effects will be critical for space applications of low Brownian-noise crystalline mirrors for precision interferometry.

Novel route is presented to manufacture high reflection coatings using only SiO2 material and GLAD method. A numerous analyses indicate the superior properties of all-silica coatings when compared with standard methods for Bragg mirrors production.

High-intensity laser–plasma interactions produce a wide array of energetic particles and beams with promising applications. Unfortunately, the high repetition rate and high average power requirements for many applications are not satisfied by the lasers, optics, targets, and diagnostics currently employed. Here, we aim to address the need for high-repetition-rate targets and optics through the use of liquids. A novel nozzle assembly is used to generate high-velocity, laminar-flowing liquid microjets which are compatible with a low-vacuum environment, generate little to no debris, and exhibit precise positional and dimensional tolerances. Jets, droplets, submicron-thick sheets, and other exotic configurations are characterized with pump–probe shadowgraphy to evaluate their use as targets. To demonstrate a high-repetition-rate, consumable, liquid optical element, we present a plasma mirror created by a submicron-thick liquid sheet. This plasma mirror provides etalon-like anti-reflection properties in the low field of 0.1% and high reflectivity as a plasma, 69%, at a repetition rate of 1 kHz. Practical considerations of fluid compatibility, in-vacuum operation, and estimates of maximum repetition rate are addressed. The targets and optics presented here demonstrate a potential technique for enabling the operation of laser–plasma interactions at high repetition rates.

Efficiency of optoelectronic devices can be enhanced by using Distributed Bragg Reflector (DBR). Distributed Bragg Reflector (DBR) is a multipair layered structure of high and low refractive indices. High reflectivity of DBR is due to constructive interference of reflected light from interfacial layers of DBR. In the present paper, reflectivity of DBR composed of II-VI compound semiconductor is simulated using Transfer Matrix Method (TMM). In this paper, reflectivity of 4, 8, 12, 16 and 20 periods for the incidence angle of 45+ is simulated. Also, the effect of interchange of constituent layers in DBR stack, on reflectivity is simulated.

Silver-based highly-reflective coatings are widely used in the manufacture of optical instruments. However, it is still difficult to achieve both high reflectivity and long-term stability of the protected silver-based mirrors simultaneously. Here the thermal stability of silver-based high reflectance coatings is investigated both theoretically and experimentally. Silver-based mirrors are annealed at different temperatures, and then are characterized by X-ray diffraction and UV-VIS spectrophotometer. The microstructure of Ag-Cu alloy film is affected by the annealing temperature, which leads to the decreasing of reflectance of the alloy film with the increasing of annealing temperature obviously.