The alleged observation of traces of inflation of the Universe in CMB spectra was later ascribed to the scattering from the space dust (BICEP2, 2018). Hence, the development of experimental methods, which distinguish between light from objects with a similar color temperature and polarization presents an important practical problem. In this paper, we discuss the proposal to discriminate between objects with the same color temperature but having different angular spectrums by intensity interferometry. The two-point correlation function of the black body image with extended angular spectrum has significant differences with a correlation function of a black body with a narrow angular spectrum.
We provide a quantitative theory of discrimination between objects with the same color temperature but having different angular spectrum by intensity interferometry. The twopoint correlation function of the black body image with extended angular spectrum has significant differences with a correlation function of a black body with a narrow angular spectrum.
One of the problems of energy harvesting with nanoantennas is a limited coherence length of solar or any other greybody radiation. In our previous paper on the subject, we proposed using Talbot effect to enhance, potentially indefinitely, the coherence length of blackbody radiation. Current paper extends this result by providing a theory, which takes into account a finite aperture of incipient beam. In this context we must mention that for monochromatic laser beam, the transmission through a correctly placed second grating completely restores coherence, smeared by the first grating. Because of an extended spectral range of blackbody radiation, complete reconstruction of an image obtained by metamaterial propagation is not possible and additional structures appear in a beam. We try to demonstrate extra features of blackbody radiation, which appear on propagation through the periodic structures located at average Talbot distance for the emission spectrum of the source.
KEYWORDS: Black bodies, Correlation function, Solar radiation, Antennas, Solar energy, Energy harvesting, Coherence (optics), Infrared radiation, Electromagnetism, Infrared sensors
Modern technology allows the fabrication of antennas with a characteristic size comparable to the electromagnetic wavelength in the optical region. This has led to the development of new technologies using nanoscale rectifying antennas (rectennas) for solar energy conversion and sensing of terahertz, infrared, and visible radiation. For example, a rectenna array can collect incident radiation from an emitting source and the resulting conversion efficiency and operating characteristics of the device will depend on the spatial and temporal coherence properties of the absorbed radiation. For solar radiation, the intercepted radiation by a micro- or nanoscale array of devices has a relatively narrow spatial and angular distribution. Using the Van Cittert–Zernike theorem, we show that the coherence length (or radius) of solar radiation on an antenna array is, or can be, tens of times larger than the characteristic wavelength of the solar spectrum, i.e., the thermal wavelength, λT=2πℏc/(kBT), which for T=5000 K is about 3 μm. Such an effect is advantageous, making possible the rectification of solar radiation with nanoscale rectenna arrays, whose size is commensurate with the coherence length. Furthermore, we examine the blackbody radiation emitted from an array of antennas at temperature T, which can be quasicoherent and lead to a modified self-image, analogous to the Talbot-Lau self-imaging process but with thermal rather than monochromatic radiation. The self-emitted thermal radiation may be important as a nondestructive means for quality control of the array.
We present a systematic study of tunable, plasmon extinction characteristics of arrays of nanoscale antennas that have potential use as sensors, energy-harvesting devices, catalytic converters, in near-field optical microscopy, and in surfaced-enhanced spectroscopy. Each device is composed of a palladium triangular-prism antenna and a flat counterelectrode. Arrays of devices are fabricated on silica using electron-beam lithography, followed by atomic-layer deposition (ALD) of copper. Optical extinction is measured by employing a broadband light source in a confocal, transmission arrangement. We demonstrate that the plasmon resonance in the extinction may be tailored by varying lithography conditions and is modified significantly by ALD. Most important, is the ability to control the gap spacing between the two electrodes, which, along with overall size, morphology, and material properties, modifies the plasmon resonance. We employ Finite-Difference Time-Domain simulations to demonstrate good agreement between experimental data and theory and use scanning electron microscopy to correlate plasmonic extinction characteristics with changes in morphology.
We have previously presented a method for optical rectification that has been demonstrated both theoretically and experimentally and can be used for the development of a practical rectification and energy conversion device for the electromagnetic spectrum including the visible portion. This technique for optical frequency rectification is based, not on conventional material or temperature asymmetry as used in MIM or Schottky diodes, but on a purely geometric property of the antenna tip or other sharp edges that may be incorporated on patch antennas. This “tip” or edge in conjunction with a collector anode providing connection to the external circuit constitutes a tunnel junction. Because such devices act as both the absorber of the incident radiation and the rectifier, they are referred to as “rectennas.” Using current nanofabrication techniques and the selective Atomic Layer Deposition (ALD) process, junctions of 1 nm can be fabricated, which allow for rectification of frequencies up to the blue portion of the spectrum (see Section 2).
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