Active cavity absolute radiometer based on high-T_csuperconductors

Abstract

To implement the detector-based radiometric scale in the new Medium Background Infrared (MBIR) facility at the National Institute of Standards and Technology (NIST), we have developed an electrical substitution cavity radiometer that can be operated just above liquid nitrogen temperature. This MBIR Active Cavity Radiometer (ACR) utilizes a temperature-controlled receiver cone and an independently temperature-controlled heat sink. Being a thermal-type detector, low noise and drift of the radiometer signal depends mainly on low-noise temperature control of the receiver and heat sink. Using high critical-temperature (T c) superconducting thin film temperature sensors in the active control loops, we have achieved closed-loop temperature controllability of better than 10 µK at 89 K for a receiver having an open-loop thermal time constant of about 75 seconds. For a flux level of 1 µW to 10 µW, the rms noise floor over a measurement cycle time is below 20 nW. This is the lowest noise level yet reported for a liquid nitrogen cooled electrical-substitution radiometer, and it is the first demonstration of the use of high-T c superconductors in such a radiometer. Potential uses for this ACR in the MBIR facility include absolute measurement of the broadband radiance of large-area 300 K cryogenic blackbody sources, and absolute measurement of the spectral radiance of laser-illuminated integrating spheres for improved relative spectral responsivity measurements of infrared transfer standard radiometers.

Smart Bolometer: Toward Monolithic Bolometer with Smart Functions

“…This additional resistor has to be close to the sensing resistor, which adds a constraint to the design of the bolometer. Operation in closed-loop mode using this configuration is successfully demonstrated in (Rice et al, 1998;Allègre et al, 2007).…”

“…5(c), uses an additional resistor (R H ) as a heater to produce the Joule heating stimuli (Rice et al, 1998). It enables the separation between the electrical and the thermal operation points at the expense of an additional resistor.…”

Achieving 0.1% radiometric uncertainty in the solar bands using FTS

“…One enabling technology that made NIST in Space possible was the development of a very sensitive un-cooled active cavity radiometer [10], as illustrated in Figure 2. The ACR is a thermal detector consisting of a cone-shaped absorbing receiver that is thermally coupled to a heat sink.…”

Noise Modelling of Absolute High-Tc Superconducting Measuring Instrument for X-ray Synchrotron Radiation

“…One of detection methods for absolute power of incident radiation is transformation of radiant energy to the thermal one with subsequent measurement of the sensitive element temperature [1][2]. The present paper offers the development of an absolute power measuring instrument (or radiometer) cooled by liquid N 2 for the absorbed soft X-rays power based on high-T c superconducting HTS bolometer [3].…”