Thermal Photons Research Articles

The gamma quanta absorption due to interaction to the thermal bremsstrahlung of hot gas in spheroidal galaxy cluster

The interaction of high energy gamma quantum to thermal bremsstrahlung photons of hot intracluster gas with producing electron-positron pair is considered. It is supposed that gas temperature and electron number density have spheroidal distribution in galaxy cluster. The dependence of optical depth on eccentricity and orientation of spheroid is considered.

Exploring hot QCD matter via direct photons at ALICE

We review ALICE results on direct photon production in pp, pA and AA collisions and compare them to predictions of NLO pQCD calculations, hydrodynamic, and transport models. In pp and pA collisions the measured direct photon yield is consistent with NLO pQCD calculations, scaled with the number of binary collisions. In Pb-Pb collisions an additional direct photon contribution is observed at low pT < 4 GeV/c which can be interpreted as a thermal direct photon contribution. The measured yield is larger than predictions of hydrodynamic models, but still consistent with them within uncertainties. The elliptic collective flow of direct photons was measured in central and mid-central Pb–Pb collisions and compared with hydrodynamic model predictions.

Study of neutral meson production with photon conversions in the MPD experiment at NICA

The MPD experiment is aimed to study strongly interacting matter in nucleus-nucleus collisions at the future NICA collider in the energy range 4-11 GeV per nucleon pair. Neutral pion and η measurements via two-photon decays will allow the MPD experiment to extend the variety of registered particle species and will provide important information on dynamics and properties of the medium created in heavy ion collisions at NICA energies. The measurement of neutral pion and η meson spectra is also important as a first step towards the analysis of thermal photons sensitive to the temperature of the produced medium. In this contribution, the feasibility of neutral meson production measurements in the two-photon channel via photon conversions will be presented, and implications for the study of thermal photons will be discussed.

Testing thermal photon and dilepton rates

We confront the thermal NLO vector spectral function (both the transverse and longitudinal channel with respect to spatial momentum, both above and below the light cone) with continuum-extrapolated lattice data (both quenched and with Nf = 2, at T ∼ 1.2Tc). The perturbative side incorporates new results, whose main features are summarized. The resolution of the lattice data is good enough to constrain the scale choice of αs on the perturbative side. The comparison supports the previous indication that the true spectral function falls below the resummed NLO one in a substantial frequency domain. Our results may help to scrutinize direct spectral reconstruction attempts from lattice QCD.

Adiabatic Thermal Radiation Pumps for Thermal Photonics.

We control the direction and magnitude of thermal radiation, between two bodies at equal temperature (in thermal equilibrium), by invoking the concept of adiabatic pumping. Specifically, within a resonant near-field electromagnetic heat transfer framework, we utilize an instantaneous scattering matrix approach to unveil the critical role of wave interference in radiative heat transfer. We find that appropriately designed adiabatic pumping cycling near diabolic singularities can dramatically enhance the efficiency of the directional energy transfer. We confirm our results using a realistic electronic circuit setup.

High-Temperature Polaritons in Ceramic Nanotube Antennas.

High-temperature thermal photonics presents unique challenges for engineers as the database of materials that can withstand extreme environments are limited. In particular, ceramics with high temperature stability that can support coupled light-matter excitations, that is, polaritons, open new avenues for engineering radiative heat transfer. Hexagonal boron nitride (hBN) is an emerging ceramic 2D material that possesses low-loss polaritons in two spectrally distinct mid-infrared frequency bands. The hyperbolic nature of these frequency bands leads to a large local density of states (LDOS). In 2D form, these polaritonic states are dark modes, bound to the material. In cylindrical form, boron nitride nanotubes (BNNTs) create subwavelength particles capable of coupling these dark modes to radiative ones. In this study, we leverage the high-frequency optical phonons present in BNNTs to create strong mid-IR thermal antenna emitters at high temperatures (938 K). Through direct measurement of thermal emission of a disordered system of BNNTs, we confirm their radiative polaritonic modes and show that the antenna behavior can be observed even in a disordered system. These are among the highest-frequency optical phonon polaritons that exist and could be used as high-temperature mid-IR thermal nanoantenna sources.

Thermal spin photonics in the near-field of nonreciprocal media

The interplay of spin angular momentum and thermal radiation is a frontier area of interest to nanophotonics as well as topological physics. Here, we show that a thick planar slab of a nonreciprocal material, despite being at thermal equilibrium with its environment, can exhibit nonzero photon spin angular momentum and nonzero radiative heat flux in its vicinity. We identify them as the persistent thermal photon spin and the persistent planar heat current respectively. With a practical example system, we reveal that the fundamental origin of these phenomena is connected to the spin-momentum locking of thermally excited evanescent waves. We also discover spin magnetic moment of surface polaritons that further clarifies these features. We then propose an imaging experiment based on Brownian motion that allows one to witness these surprising features by directly looking at them using a lab microscope. We further demonstrate the universal behavior of these near-field thermal radiation phenomena through a comprehensive analysis of gyroelectric, gyromagnetic and magneto-electric nonreciprocal materials. Together, these results expose a surprisingly little explored research area of thermal spin photonics with prospects for new avenues related to non-Hermitian topological photonics and radiative heat transport.

THE THERMAL RADIATION IMPACT OF A CURRENT CARRYING CONDUCTOR AND A METALLIC OBJECT: A CASE STUDY OF TRANSFORMER G&amp; P ACCESSORIES AND ALUMINUM LADDER

The thermal radiation impact of a current carrying conductor and a metallic object cannot be neglected. The improper knowledge of this effect and the causes are one of the major reasons that contribute to the high number of electrocution cases registered in Nigeria at various levels. This research reveals the neglected magnetic effect that exist around a current carrying conductor and a metallic object near it as one of the silent causes of electric hazard that kill people on daily basis. The researcher observered that electrons are readily available on Aluminum ladder and that photon energy from sunlight or thermal radiation usually powers this electron on the metallic ladder without the knowledge of the operator thereby causing current to start flowing on both the ladder and the current carrying conductor in the same direction. This phenomenon causes current to start flowing on the two naked conductors without the knowledge of some operators who thought that current is only flowing on transformer accessories (G and P unit). The force of attraction acts on two conductors carrying current in the same direction. For this reason, the current from photon energy (thermal radiation) and electrons flow spontaneously in all directions thereby attracting the current that flows from transformer accessories (G and P unit) placed 5 meters distance from the Aluminum ladder. The magnetic impact of this explanation is very deadly as it could result to what is known as electrocution. The researcher recommended the possible way of reducing electrical hazard that might arise from such incidence. Thermal radiation can lead to “Switching –ON” of a device to supply current when the majorities of the number of holes are equals to the no of electrons. Thermal radiation can equally leads to “Switching Off” of a device to stop supplying current when the no of holes is less than number of electrons. Naturally, every semiconductor material has a good reasonable no of electrons existing on the surface of that material and the sunlight is a good carrier of photon. Keywords : Thermal radiation, Magnetic impact, conductor, electrocution, Photon energy and transformer accessories, semiconductor material. DOI : 10.7176/APTA/80-07 Publication date :October 31 st 2019

Probing the non-Planckian spectrum of thermal radiation in a micron-sized cavity with a spin-polarized atomic beam

It is commonly thought that thermal photons with transverse electric polarization cannot exist in a planar metallic cavity whose size $a$ is smaller than the thermal wavelength $\lambda_T$, due to absence of modes with $\lambda < 2a$. Computations based on a realistic model of the mirrors contradict this expectation, and show that a micron-sized metallic cavity is filled with non-resonant radiation having transverse electric polarization, following a non-Planckian spectrum, whose average density at room temperature is orders of magnitudes larger than that of a black-body. We show that the spectrum of this radiation can be measured by observing the transition rates between hyperfine ground-state sub-levels $1S_{1/2}(F,m_F) \rightarrow 1S_{1/2}(F',m'_F)$ of D atoms passing in the gap between the mirrors of a Au cavity. Such a measurement would also shed light on a puzzle in the field of dispersion forces, regarding the sign and magnitude of the thermal Casimir force. Recent experiments with Au surfaces led to contradictory results, whose interpretation is much controversial.

(Invited) Programming Thermal Energy Transport in Semiconductor Nanowires

The confinement of mid-infrared light in deep subwavelength volumes offers exciting opportunities to control the transport of thermal energy. This talk will describe our recent efforts to program the synthesis and understand the properties of semiconductor nanowires containing chains of mid-infrared plasmonic resonators. I will discuss (i) how the programming of dopant profile enables designer thermal photon absorbers, (ii) that combining the dielectric properties of semiconductors and the 1-D geometry of nanowires leads to very strong near-field interactions, and (iii) that these interactions allow photons to carry as much heat as electrons and phonons in the solid state.

Time dependence of the thermal-photon thermometer

A systematic study of the thermal-photon thermometer is presented for heavy-ion collisions at intermediate energies via the isospin-dependent quantum molecular dynamics model. We find that the duration of the thermal hard photons production is more than $500\phantom{\rule{0.28em}{0ex}}\mathrm{fm}/c$. The divergence between the initial temperature and the final measurement temperature is about 5%. The isospin dependence of the nuclear temperature is consistent between the initial temperature and the final measurement temperature. As a comparison, the slope and double-isotope ratio thermometers are also discussed.

Ultraefficient thermophotovoltaic power conversion by band-edge spectral filtering

Thermophotovoltaic power conversion utilizes thermal radiation from a local heat source to generate electricity in a photovoltaic cell. It was shown in recent years that the addition of a highly reflective rear mirror to a solar cell maximizes the extraction of luminescence. This, in turn, boosts the voltage, enabling the creation of record-breaking solar efficiency. Now we report that the rear mirror can be used to create thermophotovoltaic systems with unprecedented high thermophotovoltaic efficiency. This mirror reflects low-energy infrared photons back into the heat source, recovering their energy. Therefore, the rear mirror serves a dual function; boosting the voltage and reusing infrared thermal photons. This allows the possibility of a practical >50% efficient thermophotovoltaic system. Based on this reflective rear mirror concept, we report a thermophotovoltaic efficiency of 29.1 ± 0.4% at an emitter temperature of 1,207 °C.

Charge-photon transport statistics and short-time correlations in a single quantum dot–resonator system with an arbitrarily large coupling parameter

Electrical quantum conductors coupled to microwave resonators have in the last decade emerged as a versatile testbed for controllable light-matter interaction on the nanometer scale. Recent experimental progress with high impedance resonators has resulted in conductor-resonator systems with a large, dimensionless coupling parameter $\lambda \gtrsim 0.1$, well beyond the small coupling regime $\lambda \ll 1$. Motivated by this progress, we here analyse theoretically the joint statistics of transported electrons and emitted photons in a single level quantum dot coupled to a microwave resonator, for arbitrarily large $\lambda$. Describing the electron-photon dynamics via a number-resolved master equation, we evaluate the joint long-time probability distribution as well as joint short-time, $g^{(2)}(t)$, correlation functions. Considering the high-bias regime, with sequential electron tunneling and working in the damping basis, allows us to obtain analytical results for both transport cumulants and $g^{(2)}(t)$ functions. It is found that the photons emitted out of the resonator are bunched and display a super-Poissonian statistics, for all system parameters. However, the electron transport properties are found to be unaffected by the coupling to the resonator, anti-bunched and with sub-Poissonian statistics. From the joint distribution we identify regimes of electron tunneling induced photon cascades and very large $g^{(2)}(t)$ functions. All $g^{(2)}(t)$-functions are found to be independent of $\lambda$. We also identify conditions for and transport signatures of a thermal resonator photon state.

Ionization degree and magnetic diffusivity in the primordial star-forming clouds

ABSTRACTMagnetic fields play such roles in star formation as the angular momentum transport in star-forming clouds, thereby controlling circumstellar disc formation and even binary star formation efficiency. The coupling between the magnetic field and gas is determined by the ionization degree in the gas. Here, we calculate the thermal and chemical evolution of the primordial gas by solving chemical reaction network where all the reactions are reversed. We find that at ∼1014–1018 cm−3, the ionization degree becomes 100–1000 times higher than the previous results due to the lithium ionization by thermal photons trapped in the cloud, which has been omitted so far. We construct the minimal chemical network which can reproduce correctly the ionization degree as well as the thermal evolution by extracting 36 reactions among 13 species. Using the obtained ionization degree, we evaluate the magnetic field diffusivity. We find that the field dissipation can be neglected for global fields coherent over ≳ a tenth of the cloud size as long as the field is not so strong as to prohibit the collapse. With magnetic fields strong enough for ambipolar diffusion heating to be significant, the magnetic pressure effects to slow down the collapse and to reduce the compressional heating become more important, and the temperature actually becomes lower than in the no-field case.

Rotationally driven VHE emission from the Vela pulsar

Context. The recent detection of pulsedγ-ray emission from the Vela pulsar in the ∼10 to 100 GeV range by H.E.S.S. promises important potential to probe into the very high energy (VHE) radiation mechanisms of pulsars.Aims. A combined analysis of H.E.S.S. andFermi-LAT data suggests that the leading wing of the P2 peak shows a new, hard gamma-ray component (with photon index as hard as Γ ∼ 3.5), setting in above 50 GeV and extending beyond 100 GeV. We study these findings in the context of rotationally driven (centrifugal) particle acceleration.Methods. We analyze achievable particle energies in the magnetosphere of the Vela pulsar and calculate the resultant emission properties.Results. Inverse Compton up-scattering of thermal photons from the surface of the star is shown to lead a pulsed VHE contribution reaching into the TeV regime with spectral characteristics compatible with current findings. If confirmed by further observations this could be the second case where rotationally driven processes turn out to be important to understand the VHE emission in young pulsars.

Macroscopically Aligned Carbon Nanotubes as a Refractory Platform for Hyperbolic Thermal Emitters

Refractory nanophotonics, or nanophotonics at high temperatures, can revolutionize many applications, including data storage and waste heat recovery. In particular, nanophotonic devices made from hyperbolic materials are promising due to their nearly infinite photonic density of states (PDOS). However, it is challenging to achieve a prominent PDOS in existing refractory hyperbolic materials, especially in a broad spectral range. Here, we demonstrate that macroscopic films and architectures of aligned carbon nanotubes work as excellent refractory hyperbolic materials. We found that aligned carbon nanotubes are thermally stable up to $1600^{\circ}$C and exhibit extreme anisotropy - metallic in one direction and insulating in the other two directions. Such extreme anisotropy makes this system a hyperbolic material with an exceptionally large PDOS over a broadband spectrum range (longer than $4.3\mu$m) in the midinfrared, exhibiting strong resonances in deeply sub-wavelength-sized cavities. We observed polarized, spectrally selective thermal emission from aligned carbon nanotube films as well as indefinite cavities of aligned carbon nanotubes with volume as small as $\sim\lambda^3/700$ operating at $700^{\circ}$C . These experiments suggest that aligned carbon nanotubes possess naturally large PDOS that leads to thermal photon densities enhanced by over two orders of magnitude, making them a promising refractory nanophotonics platform.

Benchmarking a nonequilibrium approach to photon emission in relativistic heavy-ion collisions

In this work, the production of photons through binary scattering processes is investigated for equilibrated hadronic systems. More precisely, a non-equilibrium hadronic transport approach to describe relativistic heavy-ion collisions is benchmarked with respect to photon emission. Cross sections for photon production in $\pi + \rho \to \pi + \gamma$ and $\pi + \pi \to \rho + \gamma$ scattering processes are derived from an effective chiral field theory and implemented into the hadronic transport approach, SMASH (Simulating Many Accelerated Strongly-interacting Hadrons). The implementation is verified by systematically comparing the thermal photon rate to theoretical expectations. Further, the impact of form factors is discussed, scattering processes mediated by $\omega$ mesons are found to contribute significantly to the total photon production. Several comparisons of the yielded photon rates are performed: to parametrizations of the very same rates, as used in hydrodynamic simulations, to previous works relying on different cross sections for the production of direct photons from the hadronic stage, and to partonic rates. Finally, the impact of considering the finite width of the $\rho$ meson is investigated, where a significant enhancement of photon production in the low-energy region is observed. This benchmark is the first step towards a consistent treatment of photon emission in hybrid hydrodynamics+transport approaches and a genuine dynamical description.

Multimessenger Implications of AT2018cow: High-energy Cosmic-Ray and Neutrino Emissions from Magnetar-powered Superluminous Transients

Abstract Newly born, rapidly spinning magnetars have been invoked as the power sources of superluminous transients, including the class of “fast blue optical transients” (FBOTs). The extensive multiwavelength analysis of AT2018cow, the first FBOT discovered in real time, is consistent with the magnetar scenario and offers an unprecedented opportunity to comprehend the nature of these sources and assess their broader implications. Using AT2018cow as a prototype, we investigate high-energy neutrino and cosmic-ray production from FBOTs and the more general class of superluminous supernovae (SLSNe). By calculating the interaction of cosmic rays and the time-evolving radiation field and baryon background, we find that particles accelerated in the magnetar wind may escape the ejecta at ultrahigh energies. The predicted high-energy neutrino fluence from AT2018cow is below the sensitivity of the IceCube Observatory, and estimates of the cosmically integrated neutrino flux from FBOTs are consistent with the extreme-high-energy upper limits posed by IceCube. High-energy γ rays exceeding GeV energies are obscured for the first months to years by thermal photons in the magnetar nebula, but are potentially observable at later times. Given their potentially higher volumetric rate compared to other engine-powered transients (e.g., SLSNe and gamma-ray bursts), we conclude that FBOTs are favorable targets for current and next-generation multimessenger observatories.

A method for evaluating microwaves entanglement efficiency based on second-order correlation detection

A method for evaluating the entanglement efficiency of dual-path entangled microwaves based on second-order correlation detection is proposed in this paper. The relationship between the squeezing degree and the entanglement efficiency in the lossless case was analyzed using the second-order interference visibility as the indicator based on measurements of the signal field strength. A loss model was established to analyze the relationship between the average thermal photons, squeezing degree, and entanglement efficiency in the lossy case. The results show that in the lossless case, a larger squeezing degree leads to a lower percentage of entangled photons, giving a lower entanglement efficiency. The entanglement efficiency first increases and then decreases with the increase of the squeezing degree in the lossy case, where the maximum achievable entanglement efficiency depends on the average thermal photons. The lower number the average thermal photons, the higher the maximum achievable entanglement efficiency, and the lower the corresponding squeezing degree. The research results provide a theoretical reference to balance the entanglement degree and entanglement efficiency of industrially-prepared dual-path entangled microwaves.

Thermal photon drag in many-body systems

We demonstrate the existence of a thermal analog of Coulomb drag in many-body systems which is driven by thermal photons. We show that this frictional effect can either be positive or negative depending on the separation distances within the system. Also we highlight that the persistent heat currents flowing in non-reciprocal systems at equilibrium are subject to this effect and the latter can even amplify these flows.