Retro Reflection Research Articles

Watching the watchers: camera identification and characterization using retro-reflections

A focused imaging system such as a camera will reflect light directly back at a light source in a retro-reflection (RR) or cat-eye reflection. RRs provide a signal that is largely independent of distance providing a way to probe cameras at very long ranges. We find that RRs provide a rich source of information on a target camera that can be used for a variety of remote sensing tasks to characterize a target camera including predictions of rotation and camera focusing depth as well as cell phone model classification. We capture three RR datasets to explore these problems with both large commercial lenses and a variety of cell phones. We then train machine learning models that take as input a RR and predict different parameters of the target camera. Our work has applications as an input device, in privacy protection, identification, and image validation.

Andreev reflection in a normal-superconductor-normal junction based on type-II Weyl semimetal

The quantum transport behavior of the normal-superconductor-normal (NSN) junction is studied theoretically based on a type-II Weyl semimetal which is rotated a certain angle. The calculation results show that the orientation angle determines the scattering mechanism of the system. In the NSN junction, there exist simultaneously two local Andreev reflections (ARs) (retro AR and specular AR) and two local election transmissions (ETs) (retro ET and specular ET) when the orientation angle is small. Moreover, the retro AR is gradually suppressed with the further increase of the orientation angle. When the orientation angle exceeds the critical angle, the scattering mechanism in NSN junction is the same as that of the NSN junction in normal mental, i.e. the normal electron reflection, normal electron transmission, retro Andreev reflection and crossed Andreev reflection take place simultaneously. In addition, the total conductance of the system is unaffected by the chemical potential, nor by the incident angle when the orientation angle is smaller than the critical angle, but decreases with the increase of the incident angle when the orientation angle is greater than the critical angle. The conductance of crossed Andreev reflection increases with incident angle increasing under some conditions.

Evaluation of Outer Structure Solar Reflection Characteristics of Highly Reflective Material in Consideration of Human Thermal Sensation

As a solution to the influence of solar radiation on thermal comfort in urban streets, constructing outer surfaces with highly reflective materials is considered to be controlling the directional reflection of the materials, and to reflect most of the radiation in the retroreflective direction—the same direction as that of the incident radiation. This study experimentally and numerically evaluates the directional solar reflectance of the outer cover material having an uneven surface. There is found to be a strong impact of radiation on human thermal comfort, and reduction of this radiation is the key to improving the thermal environment. Accordingly, the use of highly reflective materials is a good strategy for enabling this improvement, and retro reflection is a promising concept to consider in this regard. The simulation results show that human thermal comfort is determined by retro reflection if solar reflectance is the same.

The satellite distance radiometer with a passive retroreflection of a request radio signal

In prospect projects of the lunar information and navigation support system, the using of a satellite range finder for solving the problem of ballistic support of near-moon spacecrafts is considered. In this paper we consider a mathematical model for calculating the radio line of a satellite rangefinder with passive retro reflection of the requested radio signal from selenodetic points. The model allows the calculation of the signal-to-noise ratio in the reflected radio signal and the standard deviation of the determination of the distance from the spacecraft to the passive radio retroreflector under various conditions. The calculations take into account both the reflection of the signal from the radio retroreflector and from the surrounding surface lunar soil. Various types of radio retroreflectors in the form of combinations of corner reflectors and in the form of a Luneburg lens are considered. The calculations of the radio line using the indicated types of retro radio reflectors for different values of the orbit height, signal frequency and other parameters are performed. It is shown that, at certain values of the parameters of the radio line, the standard deviation of the determination of the range of the order of units of meters and less is achieved both for the Luneburg lens and the combined angular reflector. The final choice should be made taking into account their mass, as well as the possibilities of transforming the radio retroreflector from transportation to working condition.

Polarization properties of calibration reflector system in the polarization-modulated space laser communication

Abstract S-polarization light and p-polarization light are mutually cross orthogonal, which can be used as signal light for emitting and receiving in the polarization-modulated space laser communication, respectively. Due to the retro reflection characteristics of the corner cube retroreflector (CCR), it is widely used as a calibration reflector system in the polarization-modulated space laser communication. The polarization states of the incident light will be change owing to the total internal reflection (TIR) of uncoated rear surface, in addition, each of the six propagation trips will in general produce a different output polarization. For the calibration reflector system in the polarization-modulated space laser communication, the polarization state of the received light, especially the intensity ratio of the p-polarization component, needs to be clarified. In this paper, a framework is presented to calculate polarization by ray tracing through CCR with arbitrary input polarization states and incident angles. On this basis, the relationships between intensity ratio of the p-polarization component in the received light of each propagation trip and the incident light with different polarization states at normal incidence as well as the circular polarized light at incident angles within ± 15°analyzed. Theoretical analysis and experiments have guiding significance for the development of the polarization-modulated space laser communication.

再帰反射性材料の施工によるヒートアイランド抑制効果の数値予測

再帰反射性材料の施工によるヒートアイランド抑制効果の数値予測

사각면 코너 큐브 재귀 반사체의 반사출력광 특성 및 응용

The applications for retro-reflectors, with their unique reflection characteristics, have been expanding, to include venetian blind slats, displays, traffic safety mark, etc. We propose expandable structures of inclined corner cube retro-reflectors and analyze their corresponding reflection characteristics. Various traffic safety structures with retro-reflectors may be designed more quantitatively using the chart of characteristics we have presented.Keywords: Geometric optics, Corner cube reflector, Retro reflection, Traffic safety, Retro-reflection characteristic chartOCIS codes: (080.0080) Geometric optics; (080.4035) Mirror system design

Nonlocal spin-entangled Andreev reflection, fractional charge, and current-phase relations in topological bilayer-exciton-condensate junctions

We study Andreev reflection and Josephson currents in topological bilayer exciton condensates (TEC). These systems can create 100% spin entangled nonlocal currents with high amplitudes due to perfect nonlocal Andreev reflection. This Andreev reflection process can be gate tuned from a regime of purely retro reflection to purely specular reflection. We have studied the bound states in TEC-TI-TEC Josephson junctions and find a gapless dispersion for perpendicular incidence. The presence of a sharp transition in the supercurrent-phase relationship when the system is in equilibrium is a signature of fractional charge, which can be further revealed in ac measurements faster than relaxation processes via Landau-Zener processes.

Retro reflection of electrons at the interface of bilayer graphene and superconductor

Electron reflection at an interface is a fundamental quantum transport phenomenon. The most famous electron reflection is the electron→hole Andreev reflection (AR) at a metal/superconductor interface. While AR can be either specular or retro-type, electron→electron reflection is limited to only the specular type. Here we show that electrons can undergo retro-reflection in bilayer graphene (BLG). The underlying mechanism for this previously unknown process is the anisotropic constant energy band contour of BLG. The electron group velocity is fully reversed upon reflection, causing electrons to be retro-reflected. Utilizing a BLG/superconductor junction (BLG/S) as a model structure, we show that the unique low energy quasiparticle nature of BLG results in two striking features: (1) AR is completely absent, making BLG/S 100% electron reflective; (2) electrons are valley-selectively focused upon retro-reflection. Our results suggest that BLG/S is a valley-selective Veselago electron focusing mirror which can be useful in valleytronic applications.