Thermal Radiation Spectrum Research Articles

A model of scattered thermal radiation for Venus from 3 to [formula omitted

Thermal radiation becomes a prominent feature in the continuum spectrum of Venus longwards of ∼3μm. The emission is traceable to the upper cloud and haze layers in the planet's mesosphere. Venus' thermal radiation spectrum is punctuated by CO2 bands of various strengths probing into different atmospheric depths. It is thus possible to invert measured spectra of thermal radiation to infer atmospheric temperature profiles and offer some insight into the cloud and haze structure. In practice, the retrieval becomes complicated by the fact that the outgoing radiation is multiply scattered by the ubiquitous aerosol particles before leaving the atmosphere. We numerically investigate the radiative transfer problem of thermal radiation from the Venus night side between 3 and 5μm with a purpose-built model of Venus' mesosphere. Special emphasis is laid on the significance of scattering. The simulations explore the space of model parameters, which includes the atmospheric temperature, cloud opacity, and the aerosols' size and chemical composition. We confirm that aerosol scattering must be taken into account in a prospective temperature retrieval, which means an additional complication to the already ill-posed retrieval problem. We briefly touch upon the degeneracy in the spectrum's shape associated with parameterization of the Venus clouds. Reasonable perturbations in the chemical composition and size of aerosols do not significantly impact the model simulations. Although the experiments are specific to the technical characteristics of the Visual and Infrared Thermal Imaging Spectrometer on the Venus Express spacecraft, the conclusions are generally valid.

Possible experimental verification of Bellert’s cosmological red shift law using the Cosmic Microwave Background Radiation

The author presents a loose proposal of an experiment of measurements of the spectrum of the local black body thermal radiation of the quantum vacuum. The experiment may verify the Bellert’s and other theories about the nature of the cosmological red shift of electromagnetic waves and give a new interpretation of measurements of Cosmic Blackbody Radiation delivered by the satellite missions COBE and WMAP. Differently to the Big Bang theory, it is assumed that the quantum vacuum continuously generates thermal noise with the spectrum given by Planck’s law.

Two infrared emission modes with different wavelengths and orthogonal polarization in a waveguide thermal emitter

This study investigates a Au/SiO2/Au waveguide thermal emitter incorporating a metallic grating embedded in the SiO2 layer. The metal grating acts as a beam splitter, dividing the device into two waveguide structures determined by the polarization of the waveguide modes. The thermal radiation spectrum exhibits two peaks with orthogonal polarization. The emitted wavelengths of the two waveguide modes can be adjusted by controlling the thickness of the SiO2 layers on both sides of the metallic grating during the fabrication process. The emission peaks have ratios of the full width at half maximum to the peak wavelength of 0.057 and 0.05 for the TE and TM polarizations, respectively. These characteristics show the suitability of the device for multi-peaks and narrow bandwidth infrared light source applications.

Electrically driven light emission from a single suspended carbon nanocoil

Electrically driven thermal radiation spectra from single suspended carbon nanocoils (CNCs) were investigated. The suspended CNC, whose structure is a hybrid between sp2 graphite-like nanocrystallites and sp3 amorphous carbon, shows thermally excited emission peaks superimposed on the blackbody radiation spectrum for wavelengths above 600nm. It is believed that at least four pairs of energy bands exist around the Fermi energy level and the observed emission peaks are attributed to thermally-excited interband electron transitions in the CNC. Photoluminescence measurements for the CNCs show similar emission peaks to the thermally excited emission, which further supports our speculation on the electronic structure of the CNC.

The Blackbody Radiation Spectrum Follows from Zero-Point Radiation and the Structure of Relativistic Spacetime in Classical Physics

The analysis of this article is entirely within classical physics. Any attempt to describe nature within classical physics requires the presence of Lorentz-invariant classical electromagnetic zero-point radiation so as to account for the Casimir forces between parallel conducting plates at low temperatures. Furthermore, conformal symmetry carries solutions of Maxwell’s equations into solutions. In an inertial frame, conformal symmetry leaves zero-point radiation invariant and does not connect it to non-zero-temperature; time-dilating conformal transformations carry the Lorentz-invariant zero-point radiation spectrum into zero-point radiation and carry the thermal radiation spectrum at non-zero temperature into thermal radiation at a different non-zero temperature. However, in a non-inertial frame, a time-dilating conformal transformation carries classical zero-point radiation into thermal radiation at a finite non-zero-temperature. By taking the no-acceleration limit, one can obtain the Planck radiation spectrum for blackbody radiation in an inertial frame from the thermal radiation spectrum in an accelerating frame. Here this connection between zero-point radiation and thermal radiation is illustrated for a scalar radiation field in a Rindler frame undergoing relativistic uniform proper acceleration through flat spacetime in two spacetime dimensions. The analysis indicates that the Planck radiation spectrum for thermal radiation follows from zero-point radiation and the structure of relativistic spacetime in classical physics.

Triple Peaks Plasmonic Thermal Emitter with Selectable Wavelength Using Periodic Block Pattern as Top Layer

A plasmonic thermal emitter with a periodic block pattern as the top layer was investigated. It is found that by adjusting the length and orientation of the rectangle metallic islands inside the block pattern, three polarization-dependent peaks can be obtained in the thermal radiation spectra. The individual mode can be extracted according to the different polarizations by an external polarizer. In addition, the device can be designed to emit in the desired wavelength range by tuning the dimensions of the block pattern.

PHOTOSPHERIC THERMAL RADIATION FROM GRB COLLAPSAR JETS

We have performed 2D relativistic hydrodynamic simulations of jets from a collapsar. The light curves and spectrum of the photospheric thermal radiation from ultrarelativistic gamma-ray burst (GRB) jets are calculated by the post process. At the head the jet has a dissipated region in which internal shocks can be seen and a freely expanding region follows. The freely expanding region shows a bullet like shape. The light curves continue about 100 s which corresponds to the jet injection duration. The light curves for θv ≤ 2° show quick rise and time variability for the first phase and low and steady luminosity phase follows. The light curves for θv ≥ 3° show slow rise and low luminosity. The spectrum below the peak energy is a power law and the index is 1 ~ 2.6 which is softer than that of single temperature plank distribution Some of them are close to the observed one, i.e., Band function.

强激光毁伤过程的热辐射谱测量

The applications of spectral technologies in intense laser damage are introduced by taking the temperature retrievals of thermal radiation spectra for example.A self-made high speed spectrum measurement system is used to collect radiation spectra for intense laser damage in real-time.The damage zone temperature is obtained through the temperature retrieval based on the principle of Planck′s black body radiation,and the temperature distribution of a damage zone is calculated by using the principal component regression.The measurements of transient temperature and temperature distribution for intense laser irradiating targets are realized,and the spectral range is 200-1 000 nm corresponding to the temperature retrieval range for 700-6 000 ℃.

Measurements of nonstationary temperatures by the spectral pyrometry method

Recording of a sequence of thermal-radiation spectra allows determination of a nonstationary temperature T(t) without using the data on the emissivity of an object. For a КЭФ-4.5 silicon single crystal heated with radiation from a continuous-wave Nd:YAG laser (λ = 1.064 μm), sequences of hundreds of emission spectra in wavelength ranges of λ = 350–760 nm and λ = 650–1000 nm were recorded at a signal storage time of a CCD array of τ = 15–35 ms and a frequency of recording spectra of f ≈ 30–66 Hz. The spectra were automatically processed, and the dependences of the crystal temperature on the time after the irradiation onset were obtained in the range T ≈ 1100–1450 K.

Determination of temperature and emissivity of opaque heated bodies via thermal radiation spectrum: simulation of measurements in spectral window

Computer simulation of emitted radiation intensity spectrum of tantalum object was carried out. Simulation measurements occurred in a narrow spectral window, which moved along the spectrum with the given step. In this way, spectral ranges at which the dependence of the emissivity (or its logarithm) on the wavelength is the simplest and fairly accurate, in particular linear, were sought for. In the case of successful search for the specified spectral range, the required temperature was determined in the spectral window with the least squares technique. If the emissivity (or its logarithm) is linearly dependent on the wavelength then the alternative estimation of the true temperature is possible. In this case, the required temperature is determined via the change of the convexity of the spectral emissivity dependence at selection of its numerical value from the values lower than the true temperature value to the values higher than the true temperature value. This approach is simple, does not require solution of the system of equations and can significantly narrow temperature range to which the true temperature belongs.

Thermal conductivity of a single carbon nanocoil measured by field-emission induced thermal radiation

The spectrum of thermal radiation induced by field emission from a single carbon nanocoil (CNC) is obtained, from which its thermal conductivity is investigated. It is found that the resistivity of the CNC shows an exponential decrease with increasing temperature. The spectrum calculated by the temperature distribution along the CNC coincides with that calculated by the single maximum temperature in the wavelength range below 1250 nm, but shows considerable differences in intensity and peak position for higher wavelengths. Based on this understanding, the thermal conductivity of the CNC is evaluated to be 38 W/m K by a one-dimensional thermal conduction model.

Extension of Planck's law of thermal radiation to systems with a steady heat flux

Planck's law of thermal radiation is limited to equilibrium systems that have a definite temperature and do not carry any heat flux. Here we extend it to steady-state systems with a constant heat flux. The obtained formulas explicitly describe the spectrum of thermal radiation in every direction and provide a sound basis for the self-consistent analysis of radiative heat transport across interfaces, gaps, layered and other important structures.

THERMAL RADIATION FROM GAMMA-RAY BURST JETS

In this study, the light curves and spectrum of the photospheric thermal radiation from ultrarelativistic gamma-ray burst (GRB) jets are calculated using 2D relativistic hydrodynamic simulations of jets from a collapsar. As the jet advances, the density around the head of the jet decreases, and its Lorentz factor reaches as high as 200 at the photosphere and 400 inside the photosphere. For an on-axis observer, the photosphere appears concave shaped due to the low density and high beaming factor of the jet. The luminosity varies because of the abrupt change in the position of the photosphere due to the internal structure of the jet. Comparing our results with GRB090902B, the flux level of the thermal-like component is similar to our model, although the peak energy looks a little bit higher (but still within a factor of 2). From the comparison, we estimate that the bulk Lorentz factor of GRB090902B is $\Gamma \sim 2.4 \times 10^2 (r/10^{12} \rm cm$) where $r$ is the radius of the photosphere. The spectrum for an on-axis observer is harder than that for an off-axis observer. There is a time lag of a few seconds for high energy bands in the light curve. This may be the reason for the delayed onset of GeV emission seen in GRB080916C. The spectrum below the peak energy is a power law and the index is $2.3 \sim 2.6$ which is softer than that of single temperature plank distribution but still harder than that of typical value of observed one.

Radiation Thermometry Based on Photonic Crystal Fiber

Fiber-coupled radiometry allows for the radiometric measurement of high temperatures in environments where there is no line of sight to the target. However, transmission through conventional silica optical fibers degrades rapidly at elevated temperatures, and exotic fibers—such as sapphire fibers—typically cannot be bent. As part of a project to investigate the performance of solid oxide fuel cells, the feasibility of using an alternative fiber, solid-core silica photonic crystal fiber (PCF), was tested. The test system used an Inconel blackbody as a source, and a detection system based on an InGaAs array spectrometer with a wavelength range of 907 nm to 1681 nm. The temperature was determined from the spectrometer signal at particular wavelengths using the Planck relationship. Two tests were performed: (1) long-term high temperature soak tests to measure the drift and noise in thermal radiation levels, in which spectra are sequentially recorded over a long period of time with the blackbody cavity at a constant temperature and (2) temperature dependence tests, whereby thermal radiation spectra are recorded with the blackbody cavity at several temperatures. At 934 °C, the transmission of the PCF decreased at a rate of 0.078 % per hour corresponding to a temperature error of −0.12 °C per hour. The transmission of conventional silica fiber decreased at a rate of 0.5 % per hour corresponding to a temperature error of −0.8 °C per hour. While the PCF represents a significant improvement over conventional fiber, it is still not good enough for most practical purposes. At 600 °C there was no observable decline in transmission and there may be applications for PCF in that regime.

Promotion of hydrogen production using spectrally controlled thermal radiation

By controlling the thermal radiation spectrum using surface grating technologies, we promote the methane steam reforming to produce hydrogen. We fabricated a two-dimensional surface grating to tune its thermal emittance peak to the vibrational absorption bands of methane and water. We demonstrated that hydrogen production strongly depends on the spectral intensity within the resonant wavelength range, and that the hydrogen production rate is four times greater than that obtained when the spectrally controlled thermal radiation is not tuned to vibrational resonances. The optical excitation of the vibrational energy levels of gas molecules is found to effectively promote hydrogen production.

Hawking Radiation by Kerr Black Holes and Conformal Symmetry

The exponential blueshift associated with the event horizon of a black hole makes conformal symmetry play a fundamental role in accounting for its thermal properties. Using a derivation based on two-point functions, we show that the full spectrum of thermal radiation of scalar particles by Kerr black holes can be explicitly derived on the basis of a conformal symmetry arising in the wave equation near the horizon. The simplicity of our approach emphasizes the depth of the connection between conformal symmetry and black hole radiance.

Narrow bandwidth and highly polarized ratio infrared thermal emitter

Polarized infrared thermal emitters consisting of a waveguide thermal emitter combined with silver grating structure were studied. For a device containing a perforated silver film under the grating, polarized infrared light was emitted only when the wavelength satisfied the standing wave condition, therefore the broad bandwidth SiO2 phonon vibration modes were suppressed in the thermal radiation spectrum. The polarized ratio with different grating thickness was investigated and the highly polarized ratio up to 0.875 was achieved. This study demonstrated that the integrated structure can be used as a narrow bandwidth and highly polarized ratio infrared light source.

Spectral pyrometry of objects with a nonuniform temperature

The temperature of transparent gas flame (T ≈ 1900 K) is determined from the thermal radiation spectrum without using emittance data. The relation connecting the values of temperature calculated from the integrated spectrum of the entire glowing region of the flame with the maximal and arithmetic mean value is considered. Simulation is used to prove that the difference between the measured and maximal temperatures of a nonuniformly heated object in the Wien spectrum detection region does not exceed 10%.

Optimal parameterization of the spectra of outgoing thermal radiation with the data of the IKFS-2 spaceborne IR sensing device taken as an example

From the ensemble of the calculated spectra of the outgoing thermal radiation in the 660- to 2010-cm−1 range (2311 realizations) simulating global measurements by the IKFS-2 spaceborne device, the informativeness of the measurements of the outgoing thermal radiation has been analyzed in terms of Kozlov’s data volume, the degrees of freedom, and the Shannon information gain. In the entire spectral range (660–2010 cm−1), there are 106 independent parameters in the measurements of the outgoing radiation. The accuracy of the optimal parameterization of the spectral behavior of the radiation based on the radiation resolution into eigenvectors of the spectral covariance matrix has been analyzed. It is shown that to reach an rms error of the parameterization comparable with the random measurement noise for different spectral regions, it is sufficient to use from 20 to 50 first eigenvectors.

Derivation of the Planck spectrum for relativistic classical scalar radiation from thermal equilibrium in an accelerating frame

The Planck spectrum of thermal scalar radiation is derived suggestively within classical physics by the use of an accelerating coordinate frame. The derivation has an analogue in Boltzmann's derivation of the Maxwell velocity distribution for thermal particle velocities by considering the thermal equilibrium of noninteracting particles in a uniform gravitational field. For the case of radiation, the gravitational field is provided by the acceleration of a Rindler frame through Minkowski spacetime. Classical zero-point radiation and relativistic physics enter in an essential way in the derivation which is based upon the behavior of free radiation fields and the assumption that the field correlation functions contain but a single correlation time in thermal equilibrium. The work has connections with the thermal effects of acceleration found in relativistic quantum field theory.