Absolute Radiometer Research Articles

Primary realization of spectral responsivity in the near infrared using a laser-driven light source

Abstract The National Research Council (NRC) Canada has realized the spectral responsivity scale from 900 nm to 1600 nm using a Xe-based laser driven light source, double subtractive monochromator system, and an absolute cryogenic radiometer. An NRC-designed InGaAs sphere transfer standard radiometer was calibrated with combined relative standard uncertainties below 0.135 % (k=1). The scale realization was also performed with a 100 W tungsten lamp, as previously done at NRC. Calibration results and uncertainties in spectral responsivity measurements with each broadband light source are compared and presented.

Indoor Direct Comparison between High-Accuracy Pyrheliometer and Room Temperature Absolute Radiometer

Abstract This article proposes a practicable indoor method by directly comparing the pyrheliometer with the room temperature absolute radiometer (RTAR) to overcome the inconvenience of outdoor pyrheliometer calibration caused by the limitation of weather conditions. The RTAR serves as the primary standard for radiant power, irradiance, illuminance, and candela at the Center for Measurement Standards/ITRI. Given that the RTAR and pyrheliometer exhibit different sensitivity curves, the key to a successful comparison lies in designing an incident beam that enables both the RTAR and pyrheliometer to operate within their respective uniform sensitivity regions. While the indoor incident beam’s irradiance is considerably lower than solar radiation, the comparison results demonstrate a quite well measurement consistence between the RTAR and the pyrheliometer. As the indoor method is insusceptible to weather, the complex data acquisition procedures for the outdoor method can be simplified due to the stable incident beam indoors. Despite current documentary standards recommending outdoor calibration and comparison for pyrheliometer, the indoor method presented in this article can serve as a supplementary approach for assessing the accuracy of pyrheliometers during the intervals between two calibration or comparison events.

Constraining the Clustering and 21 cm Signature of Radio Galaxies at Cosmic Dawn

The efficiency of radio emission is an important unknown parameter of early galaxies at cosmic dawn, as models with high efficiency have been shown to modify the cosmological 21 cm signal substantially, deepening the absorption trough and boosting the 21 cm power spectrum. Such models have been previously directly constrained by the overall extragalactic radio background, as observed by Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission 2 and Long Wavelength Array. In this work, we constrain the clustering of high-redshift radio sources by utilizing the observed upper limits on arcminute-scale anisotropy from the Very Large Array at 4.9 GHz and Australia Telescope Compact Array at 8.7 GHz. Using a seminumerical simulation of a plausible astrophysical model for illustration, we show that the clustering constraints on the radio efficiency are much stronger than those from the overall background intensity by a factor that varies between 18 and 55 in the redshift range of 7–22. As a result, the predicted maximum depth of the global 21 cm signal is lowered by a factor of 6 (to 1400 mK), and the maximum 21 cm power spectrum peak at cosmic dawn is lowered by a factor of 45 (to 1.3 × 105 mK2). We conclude that the observed clustering is the strongest current direct constraint on such models, but strong early radio emission from galaxies remains viable for producing a strongly enhanced 21 cm signal from cosmic dawn.

Inverse Gertsenshtein effect as a probe of high-frequency gravitational waves

We apply the inverse Gertsenshtein effect, i.e., the graviton-photon conversion in the presence of a magnetic field, to constrain high-frequency gravitational waves (HFGWs).Using existing astrophysical measurements, we compute upper limits on the GW energy densities ΩGW at 16 different frequency bands.Given the observed magnetisation of galaxy clusters with field strength B ∼ μG correlated on 𝒪(10) kpc scales, we estimate HFGW constraints in the 𝒪(102) GHz regime to be ΩGW ≲ 1016 with the temperature measurements of the Atacama Cosmology Telescope (ACT).Similarly, we conservatively obtain ΩGW ≲ 1013 (1011) in the 𝒪(102) MHz (𝒪(10) GHz) regime by assuming uniform magnetic field with strength B ∼ 0.1 nG and saturating the excess signal over the Cosmic Microwave Background (CMB) reported by radio telescopes such as the Experiment to Detect the Global EoR Signature (EDGES), LOw Frequency ARray (LOFAR), and Murchison Widefield Array (MWA), and the balloon-borne second generation Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE2)with graviton-induced photons. The upcoming Square Kilometer Array (SKA) can tighten these constraints by roughly 10 orders of magnitude, which will be a step closer to reaching the critical value of ΩGW = 1 or the Big Bang Nucleosynthesis (BBN) bound of ΩGW ≃ 1.2 × 10-6.We point to future improvement of the SKA forecast and estimate that proposed CMB measurement at the level of 𝒪(100-2) nK, such as Primordial Inflation Explorer (PIXIE) and Voyage 2050, are needed to viably detect stochastic backgrounds of HFGWs.

Disentangling the anisotropic radio sky: Fisher forecasts for 21 cm arrays

ABSTRACT The existence of a radio synchrotron background (RSB) excess is implied by a number of measurements, including excess emission seen by the Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE 2) and Long Wavelength Array (LWA) experiments. Highly sensitive wideband radio arrays, of the kind used to measure the cosmic 21 cm signal, provide a promising way to further constrain the RSB excess through its anisotropy, providing additional insight into its origin. We present a framework for evaluating the potential of 21 cm arrays to disentangle different components of the diffuse radio sky based on the combination of their frequency spectrum and angular power spectrum. The formalism is designed to calculate uncertainties due to the intrinsic cosmic variance alone or together with instrumental noise. In particular, we predict the potential for measuring the anisotropy of a broad generalized class of excess radio background models using the low-frequency Hydrogen Epoch of Reionization Array (HERA) as an example. We find that a HERA-like array can distinguish an RSB excess from other sky components based on its angular clustering and spectral dependence, even if these are quite similar to one or more of the other components – but only in the case that the RSB excess is relatively bright.

Progress in Development of Radiometric Benchmark Payload of Solar Reflected Waveband Traced to Space Cryogenic Absolute Radiometer (Invited)

Progress in Development of Radiometric Benchmark Payload of Solar Reflected Waveband Traced to Space Cryogenic Absolute Radiometer (Invited)

Study of self-calibrating photodiodes for trap detectors

In accordance with the stated purpose of the study, the measurements and analysis of photodiodes were carried out, and the best alternative for the development of the trap detector was chosen. The paper substantiates the necessity for an alternative to the absolute cryogenic radiometer because of its highly expensive measurements. The need for more accurate measurement data has determined the use of trap detectors, including self-calibrating photodiodes. Such trap detectors can be used independently, without calibration by an absolute cryogenic radiometer. Thus, the cost of the study is reduced. Besides, the given approach does not affect the accuracy of the obtained measurement results.
 When reviewing modern approaches to the use of the above-mentioned trap detectors, it was discovered that trap detectors, together with self-calibrating photodiodes, are widely used both in state measurements of photometric quantities and for laboratory needs in many developed countries worldwide. The given analysis allows us to assert that the issues of developing, studying, and using new trap detectors, considering a significant advantage in their characteristics in comparison with the previously developed ones, make up an urgent scientific task.
 The paper defines selection criteria based on certain characteristics of photodiodes. When investigating the operating spectral range of the selected photodiodes, their internal quantum efficiency, geometrical dimensions of the receiving element of the selected photodiodes, and the coefficient of mirror and diffuse reflection of the receiving surface of the selected photodiodes, measurement results for all the stated characteristics were obtained. Based on these values, a screening of the photodiodes that do not meet the requirements for photodiodes specified for the development of the trap detector was made. Based on experimental studies, photodiodes S1337-1010BQ were selected.

Room Temperature Absolute Radiometer for Reproduction of Terahertz Radiant Power

We propose an electrical substitution and laser calibration technique for reproduction of terahertz radiant power. With this technique, the equivalence of terahertz absorption and electrical heating in the absorber is corrected and accurate terahertz radiant power is reproduced. A two-cavity absolute radiometer was developed for accurate reproduction of terahertz radiant power working at room temperature. The absolute radiometer has two absorptive cavities coated with different coatings. One cavity was coated with 3M Velvet-coating and used for the absolute reproduction of laser radiant power, and the other was coated with a mixture of silicon carbide particles and 3M Velvet-coating and used for the reproduction of terahertz radiant power. With the comparison of the two cavities under stable laser irradiance, the equivalence between terahertz absorption and electrical heating is calibrated, and the precision of absolute reproduction for terahertz power is improved. The reproduced power using this absolute radiometer agreed excellently with the terahertz power standard at the National Institute of Metrology, which had been used in the first international terahertz power comparison.

Spaceborne Relative Radiometer: Instrument Design and Pre-Flight Test

In order to simultaneously determine the values of total solar irradiance (TSI) and the Earth’s radiation at the top of the atmosphere (TOA) on board the Fengyun-3F satellite, a spaceborne relative radiometer (SRR) was developed. It adopts a dual-channel structure, including a solar radiometer channel (SR) with an unobstructed field of view (FOV) of 1.5° and an Earth radiometer channel (ER) with a wide field of view (WFOV) of 95.3° and a diameter of about 1900 km on the ground. Before the launch, both the SR and ER were calibrated. The SR, installed on the inner frame of the solar tracker of the SIM-II (solar irradiance monitor-II), is used to observe rapid changes in solar radiance with the SIAR (solar irradiance absolute radiometer), an electrical-substitution radiometer, on orbit. The ER is mounted on the U-shaped frame of the solar tracker, directly pointing in the nadir direction. Additionally, a dark space observation mode is used to determine the on-orbit background noise and lunar observation mode for on-orbit calibration. In this article, the instrument design and working principle of the SRR is first introduced, and an analysis of the measurement model of the ER, the WFOV channel of the SRR, is focused on. Finally, ground test results of the SRR are introduced.

The cosmic radio background from 150 MHz to 8.4 GHz and its division into AGN and star-forming galaxy flux

ABSTRACT We present a revised measurement of the extragalactic background light (EBL) at radio frequencies based on a near complete compendium of radio source counts. We present the radio-EBL at 150 MHz, 325 MHz, 610 MHz, 1.4 GHz, 3 GHz, 5 GHz, and 8.4 GHz. In all cases the contribution to the radio-EBL, per decade of flux, exhibits a two-humped distribution well matched to the active galactic nucleus (AGN) and star-forming galaxy (SFG) populations, and with each population contributing roughly equal energy. Only at 3 GHz are the source count contributions to the EBL fully convergent, and hence we report empirical lower limits to the radio-EBL in the remaining bands. Adopting predictions from the SHARK semi-analytic model for the form of the SFG population, we can fit the fainter source counts providing measurements of the total contribution to the radio-EBL for the SFG and the AGN populations separately. This constitutes an empirically constrained model-dependent measurement for the SFG contribution, but a fully empirical measurement of the AGN contribution. Using the ProSpect spectral energy distribution code we can model the ultraviolet-optical-infrared-mm-radio SFG EBL at all frequencies from the cosmic star-formation history and the adoption of a Chabrier initial mass function. However, significant discrepancy remains (5 ×) between our source-count estimates of the radio-EBL and the direct measurements reported from the Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission-2 (ARCADE-2) experiment. We can rule out a significant missing discrete source radio population and suggest that the cause of the high ARCADE-2 radio-EBL values may need to be sought either in the foreground subtraction or as a yet unknown diffuse component in the radio sky.

Long-term spectral responsivity stability of predictable quantum efficient detectors

The stability of induced junction silicon photodiodes used to construct the predictable quantum efficient detector (PQED) has been studied over a time period of a decade by measurements of its spectral responsivity against absolute cryogenic radiometers (CR) in two independent laboratories at CMI and PTB. PQEDs operated at room temperature show a long-term temporal stability within 150 ppm over a broad spectral range during a 10-year period, well within the range of the claimed measurement uncertainty values of the CRs. This long term stability fulfills one of the fundamental requirements to establish a new primary standard for the measurement of power of optical radiation.

Cosmic radiation backgrounds from primordial black holes

ABSTRACT Recent measurements of the cosmic X-ray background (CXB) and cosmic radio background (CRB) obtained with Chandra and ARCADE2 (Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission) report signals in excess of those expected from known sources, suggesting the presence of a yet undiscovered population of emitters. We investigate the hypothesis that such excesses are due to primordial black holes (PBHs) that may constitute a substantial fraction of dark matter (DM). We present a novel semi-analytical model that predicts X-ray and radio emission due to gas accretion on to PBHs, assuming that they are distributed both inside DM haloes and in the intergalactic medium (IGM). Our model includes a self-consistent treatment of heating/ionization feedback on the surrounding environment. We find that (i) the emission from PBHs accreting in the IGM is subdominant at all times ($1{{\ \rm per\ cent}} \le I_{\rm IGM}/I_{\rm tot} \le 40{{\ \rm per\ cent}}$); (ii) most of the CXB/CRB emission comes from PBHs in DM mini-haloes (Mh ≤ 106 M⊙) at early epochs ($z$ > 6). While a small fraction ($f_{\rm PBH} \simeq 0.3{{\ \rm per\ cent}}$) of DM in the form of PBHs can account for the total observed CXB excess, the CRB one cannot be explained by PBHs. Our results set the strongest existing constraint on fPBH ≤ 3 × 10−4 (30/MPBH) in the mass range of $1 \!-\! 1000 \, \mathrm{M}_\odot$. Finally, we comment on the implications of our results on the global H i 21 cm signal.

New detector for next generation solar radiometers

A new detector for solar absolute radiometers for ground-based applications was developed in a joint project by PMOD/WRC and Davos Instruments AG. New coating technology was applied and characterized, and a flat receiver was designed for the next generation of radiometers. The new detector, which is already commercially available, will also be considered and adapted for future space experiments.

Correction to: The Fengyun-3E/Joint Total Solar Irradiance Absolute Radiometer: Instrument Design, Characterization, and Calibration

Correction to: The Fengyun-3E/Joint Total Solar Irradiance Absolute Radiometer: Instrument Design, Characterization, and Calibration

Characterization of absolute cavity radiometers for traceability to SI of solar irradiance

Solar-type cavity radiometers are instruments of the highest metrological level for measuring solar direct normal irradiance. To ensure their traceability and performance, they are periodically compared to the World Group of Standards, which realizes the World Radiometric Reference (WRR), in the International Pyrheliometer Comparisons (IPCs). Additionally, they can be characterized in an absolute way, with direct traceability to SI units and with their measurement uncertainty calculated. This paper describes the different techniques and procedures applied for the characterization and calibration of solar cavity radiometers, with the main results obtained to date in the case of an Automatic Hickey–Frieden (AHF) radiometer. Voltmeters, resistors, temperature sensors and the area of the precision apertures have been calibrated, while the effective absorptance, temperature coefficients, optical scattering and non-equivalence factor have been evaluated. The temperature dependence of the electrical current in the cavity heater has also been analysed. The resulting corrections obtained for the AHF by characterization are compatible with the WRR factors obtained by this instrument in the past IPCs. An uncertainty of 0.42% (k = 1) has been obtained, and this paper discusses further improvements that may be able to reduce this figure to the desired expanded uncertainty of U = 0.1% (k = 2).

Correction to: The Fengyun-3E/Joint Total Solar Irradiance Absolute Radiometer: Instrument Design, Characterization, and Calibration

Correction to: The Fengyun-3E/Joint Total Solar Irradiance Absolute Radiometer: Instrument Design, Characterization, and Calibration

Calibration and comparison of detection efficiency for free-space single-photon avalanche diodes at 850 nm.

A detection efficiency measurement system for free-space single-photon detectors has been established at the National Research Council (NRC) Canada. This measurement apparatus incorporates an 850 nm fiber laser source and utilizes a double-attenuation and substitution calibration technique. Detection efficiency calibrations of silicon single-photon avalanche photodiodes (SPADs) at incident photon rates in the range of 1.0×105 photon counts per second (Cts/s) (36 fW) to 2.1×106Cts/s (734 fW) are SI-traceable through the substitution configuration with a silicon transfer standard detector, calibrated directly using the NRC absolute cryogenic radiometer. The measurement approach taken by the NRC was compared with the SPAD calibration technique implemented at the National Institute of Standards and Technology (NIST) in the United States. The count-rate-dependent detection efficiency of a silicon SPAD was measured at NIST and compared with results from the same SPAD measured at NRC within the range of incident photon rates from 1×105Cts/s to 5×105Cts/s. Comparison of the calibration results shows agreement between the two laboratories within the combined measurement uncertainties.

Apparatus for Calibration of Photovoltaic Cells at National Institute of Standards

The Egyptian National Institute of Standards (NIS) has established and developed a system for calibrating reference solar cells using photodiode detectors traceable to the absolute cryogenic radiometer (ACR). This research discusses an experimental procedure for measuring spectral responsivity, external quantum efficiency, and internal quantum efficiency of reference solar cells from the range of 340 nm to 930 nm. The associated uncertainty budget is also estimated. Additionally, this paper shows the NIS's calibration facility for pyranometers at different irradiance levels (200 W/m², 800W/m², and 1000W/m²). The measurement of the spectral responsivity and quantum efficiency of reference solar cells using two techniques is converged with each other with an uncertainty of about ±1% (at 900 nm). Also, the sensitivity of the pyranometer at 800W/m² is 15.97µV/W/m² ±1.9%.

Background of radio photons from primordial black holes

ABSTRACT We compute the isotropic radiation background due to Hawking emission from primordial black holes (PBHs), and examine if this background is a viable option in explaining the excess radiowave background observed by the Absolute Radiometer for Cosmology, Astrophysics and Diffuse Emission (ARCADE2) and Long Wavelength Array (LWA1) experiments at $\lesssim 1\, {\rm GHz}$. We find that even under the extreme assumption that all of the dark matter is in the form of PBHs, the radio brightness temperature induced by Hawking evaporation of PBHs is $\mathcal {O}(10^{-46})\,$K, highly subdominant compared to the cosmic microwave background. The main reason for this is that for PBHs in the mass range ∼1012–${10^{14}}\, {\rm kg}$, which can be constrained by Hawking emission, the spectrum peaks at 107 to ${10^{5}}\, {\rm eV}$. As the Hawking spectrum is power law suppressed towards lower energies, negligible flux of $\mu \mathrm{eV}$ photons is obtained. The peak of the Hawking spectrum shifts to lower energies for higher masses, but the number density is low and so is the specific intensity. Because Hawking emission from PBHs is thus unable to explain the observed excess radio background, we also consider the alternative possibility of radio emission from gas accretion on to supermassive PBHs. These PBHs can readily produce strong radio emission that could easily explain the ARCADE2/LWA1 excess.

Absolute radiation pressure detector using a diamagnetically levitating test mass

We have developed an absolute radiometer to measure laser power by means of radiation pressure in a closed control-loop configuration using diamagnetically levitated pyrolytic graphite as the soft spring and gravity as a contactless restoring force. Our approach takes advantage of an extremely low spring stiffness (2.95 mN/m) afforded by diamagnetic levitation above a permanent magnet array and a lock-in amplifier in the feedback loop to attain a 30 m W r m s noise. A horizontally directed laser beam impinges on a highly reflective dielectric stack mirror mounted on the levitating pyrolytic graphite shuttle. The light’s momentum displaces the shuttle, and its position is restored by tilting the magnet array with a piezoelectric actuator. The closed-loop configuration avoids the need for accurate knowledge of the system spring stiffness or environmental dependencies of the diamagnetic levitation. Absolute laser power measured is traceable to the mass of the diamagnetically levitating shuttle system, the local gravitational acceleration, and the interferometrically measured tilt angle of the magnet array. The system is demonstrated with a laser power of 2.7 W, yielding a combined relative expanded uncertainty ( k = 2 ) of 1.9%. The upper limit of measurable power is determined by the range of the piezoelectric actuator, and the minimum power is currently limited by the noise floor that is constrained by air currents.