We show that a perfect absorber/thermal emitter exhibiting an absorption peak of 99.9% can be achieved in metallic nanostructures that can be easily fabricated. The very high absorption is maintained for large angles with a minimal shift in the center frequency and can be tuned throughout the visible and near-infrared regime by scaling the nanostructure dimensions. The stability of the spectral features at high temperatures is tested by simulations using a range of material parameters. Since the beginning of the last century it is known that a perfect thermal emitter follows Planck’s law of blackbody radiation. 1 Realistic structures, however, generally do not follow Planck’s law but exhibit a smaller emission. The properties of these emitters strongly depend on the materials and their shapes. From the absorption spectra of a structure the emission properties can be deduced since Kirchhoff’s law directly relates the absorption with the emissivity. The emission is then determined by multiplying the emissivity with the blackbody radiation spectrum. Using photonic crystals, 2,3 it has been shown that this approach is also valid for periodically structured materials. For a number of applications such as thermophotovoltaic converters, it is necessary to control the spectral properties to achieve, e.g., selective emitters in a narrow frequency band corresponding to the band gap of solar cells. 4 In the case of structured metallic surfaces, the changes in the emission spectra are based on surface waves coupled to the external radiation through the periodic surface. 5,6 Alternatively, microcavity resonances can also be used to create narrow-band thermal radiation. 7 Unfortunately, most of the recent designs 6,8 for perfect absorbers/ emitters only work for one incident angle and one polarization. So, there is a need for wide-angle perfect absorber/ emitter nanostructures. In this Brief Report, we suggest a structure which exhibits a large absorption in the terahertz regime for a wide range of angles with respect to the surface. We show that the absorption characteristics are maintained even if the uncertainties in the estimated changes in the material parameters, due to high temperatures, are considered. The proposed structure can be easily manufactured with today’s planar microfabrication techniques. We also comment on the impact of deviations in the geometrical parameters caused by fabricational tolerances. The small size of the structure, in comparison to the wavelength together with the relatively straightforward fabrication, allows for easy integration into various devices, such as perfect thermal emitters, perfect absorbers, bolometers, and very effective light extraction light-emitting diodes LEDs. The suggested structure is shown in Fig. 1. It consists of a metal back plate black with a thickness larger than 200 nm. This is much larger than the typical skin depth in the terahertz regime and avoids transmission through the structure. In this case the reflection is the only factor limiting the absorption. The thickness of the back plate can be adjusted to the specific needs of the final application, e.g., to obtain good heat transport to sensors or to obtain a better stability. On top of the metal plate a spacer layer of silicon nitride SiN is deposited with a thickness Dt. The structure is terminated by an array of metallic stripes with a rectangular cross section. Their arrangement is described by a lattice constant a and their shape is given by a width Ww and a thickness Wt. In this setup a strong resonance with a large field enhancement in the dielectric spacer layer and in between the stripes can be obtained, as will be shown later. Adjusting the size of the metal stripes on the top, the coupling to this resonance can be tuned and the reflection can be minimized. Due to the scalability of Maxwell’s equations, in principle, the structure can be simulated using dimensionless units by dividing all sizes by the lattice constant

We demonstrate engineered selective absorption and subsequent selective thermal emission from sub-wavelength thickness optical structures at far-infrared (30–40 μm) wavelengths. Control over absorption/emission wavelength is demonstrated, with both polarization-dependent and -independent structures fabricated. Samples are characterized experimentally by Fourier transform infrared reflection and emission spectroscopy, and modeled using three-dimensional rigorous coupled wave analysis. The ability to design and demonstrate strong selective absorption and thermal emission from optical structures in the far-infrared offers a potential route towards low-cost sources for the exploration of Reststrahlen band frequencies.

Nonreciprocal elements are a vital building block of electrical and optical systems. In the infrared regime, there is a particular interest in structures that break reciprocity because their thermal absorptive (and emissive) properties should not obey the Kirchhoff thermal radiation law. In this work, we break time-reversal symmetry and reciprocity in n-type-doped magneto-optic InAs with a static magnetic field where light coupling is mediated by a guided-mode resonator structure, whose resonant frequency coincides with the epsilon-near-zero resonance of the doped indium arsenide. Using this structure, we observe the nonreciprocal absorptive behavior as a function of magnetic field and scattering angle in the infrared. Accounting for resonant and nonresonant optical scattering, we reliably model experimental results that break reciprocal absorption relations in the infrared. The ability to design these nonreciprocal absorbers opens an avenue to explore devices with unequal absorptivity and emissivity in specific channels.

Thermal radiation is electromagnetic radiation emitted by the thermal motion of particles in matter. All matter with a temperature greater than absolute Thermal radiation is electromagnetic radiation emitted by the thermal motion of particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation. The emission of energy arises from a combination of electronic, molecular, and lattice oscillations in a material. Kinetic energy is converted to electromagnetism due to charge-acceleration or dipole oscillation. At r The characteristics of thermal radiation depend on various properties of the surface from which it is emanating, including its temperature and its spectral emissivity, as expressed by Kirchhoff's law. The radiation is not monochromatic, i.e., it does not consist of only a single frequency, but comprises a continuous spectrum of photon energies, its characteristic spectrum. If the radiating body and its surface are in thermodynamic equilibrium and the surface has perfect absorptivity at all wavelengths, it is characterized as a black body. A black body is also a perfect emitter. The radiation of such perfect emitters is called black-body radiation. The ratio of any body's emission relative to that of a black body is the body's emissivity, so a black body has an emissivity of one. The absorptivity, emissivity, reflectivity, and transmissivity of all bodies are dependent on the wavelength of the radiation. Due to reciprocity, absorptivity and emissivity for any particular wavelength are equal at equilibrium – a good absorber is necessarily a good emitter, and a poor absorber is a poor emitter. The temperature determines the wavelength distribution of the electromagnetic radiation. The distribution of power that a black body emits with varying frequency is described by Planck's law. At any given temperature, there is a frequency fmax at which the power emitted is a maximum. Wien's displacement law, and the fact that the frequency is inversely proportional to the wavelength, indicates that the peak frequency fmax is proportional to the absolute temperature T of the black body. The photosphere of the sun, at a temperature of approximately 6000 K, emits radiation principally in the (human-)visible portion of the electromagnetic spectrum. Earth's atmosphere is partly transparent to visible light, and the light reaching the surface is absorbed or reflected. Earth's surface emits the absorbed radiation, approximating the behavior of a black body at 300 K with spectral peak at fmax. At these lower frequencies, the atmosphere is largely opaque and radiation from Earth's surface is absorbed or scattered by the atmosphere. Though about 10% of this radiation escapes into… A… At…

Gustav Kirchhoff Gustav Robert Kirchhoff (12 March 1824 – 17 October 1887) was a German physicist who contributed to the fundamental understanding of electrical circuits, spectroscopy, and radiation by heated objects. He coined the term black body radiation in 1862.[1] He proposed two sets of independent concepts in both circuit theory and thermal emission. They are all called 'Kirchhoff's laws' after him, as well as a law of thermochemistry. The Bunsen–Kirchhoff Award for spectroscopy is named after him and his colleague, Robert Bunsen. He also discovered rubidium with Bunsen in 1861. References - ↑ A 'black body' is an idealised physical body which absorbs all electromagnetic radiation which strikes it, and reflects none. It is also the best possible emitter of thermal radiation (heat).

general, surfaces that are good absorbers of radiation are good emitters when hot. hot copper sheet … emission of radiation, "| recall that good absorbers are also good emitters, ™ explain how a knowledge of heat … velocity 107 theories x thermal capacity 139 thermal energy see heat thermal power stations 78-9 thermals

On Radiation (Rede Lecture) For other versions of this work, see On Radiation . ← On Radiation ( 1865 ) by John Tyndall → related portals : Rede Lecture , Chemistry sister projects : Wikipedia article , Wikidata item 1412457 On Radiation 1865 John Tyndall ​ ON RADIATION. THE "REDE" LECTURE DELIVERED IN THE SENATE-HOUSE BEFORE THE UNIVERSITY OF CAMBRIDGE ON TUESDAY, MAY 16, 1865. BY JOHN TYNDALL, F.R.S. PROFESSOR OF NATURAL PHILOSOPHY IN THE ROYAL INSTITUTION AND IN THE ROYAL SCHOOL OF MINES. LONDON: LONGMAN, GREEN, LONGMAN, ROBERTS & GREEN 1865 ​ Spectrum of Electric Light. ​ CONTENTS. 1. Visible and Invisible Radiation 1 2. Origin and Character of Radiation. The Ether 6 3. The Atomic Theory in reference to the Ether 11 4. Absorption of Radiant Heat by Gases 12 5. Absorption by Iodine. Formation of Invisible Foci 18 6. Visible and Invisible Rays of the Electric Light 21 7. Combustion by Invisible Rays 24 8. Transmutation of Rays. Calorescence 27 9. Deadness of the Optic Nerve to the Calorific Rays 30 10. Persistence of Rays 33 11. Absorption of Radiant Heat by Vapours and Odours 38 12. Aqueous Vapour in relation to Terrestrial Temperatures 41 13. Liquids and their Vapours in relation to Radiant Heat 45 14. Reciprocity of Radiation and Absorption 48 15. Influence of Vibrating Period and Molecular Form. Physical Analysis of the Human Breath 52 16. Summary and Conclusion 57 ​ ON RADIATION. 1. Visible and Invisible Radiation. Between the mind of man and the outer world are interp