Optical fibre-coupled cryogenic radiometer with carbon nanotube absorber

Abstract

A cryogenic radiometer was constructed for direct-substitution optical-fibre power measurements. The cavity is intended to operate at the 3 K temperature stage of a dilution refrigerator or 4.2 K stage of a liquid cryostat. The optical fibre is removable for characterization. The cavity features micromachined silicon centring rings to thermally isolate the optical fibre as well as an absorber made from micromachined silicon on which vertically aligned carbon nanotubes were grown. Measurements of electrical substitution, optical absorption and temperature change indicate that the radiometer is capable of measuring a power level of 10 nW with approximate responsivity of 155 nW K −1 and 1/e time constant of 13 min. An inequivalence between optical and electrical power of approximately 10% was found, but the difference was largely attributable to unaccounted losses in the optical fibre.

Planar electrical-substitution carbon nanotube cryogenic radiometer

“…The resulting macroscopic cavity limits the minimum size and therefore the minimum time constant of a radiometer. While cavities can be miniaturized [2,3], cavity-based hand-assembled radiometers are labor-intensive to assemble and difficult to reproduce.…”

Measuring absolute spectral radiance using an erbium-doped fiber amplifier

“…In a metrology laboratory, an absolute standard such as a cryogenic radiometer can achieve accuracies of 10 −4 for visible collimated laser radiation [1]. Fiber-coupled systems have also been demonstrated [2][3][4]. This type of experiment however requires considerable time and effort and is usually not available at the site where the measurement is needed.…”

Towards a fiber-coupled picowatt cryogenic radiometer

“…However, there are many emerging industries that use detectors and sources operating at much lower power levels, whose calibration typically requires a chain of measurements to tie to existing primary detector standards or high dynamic range source standards that are not widely available [3,4]. Though there are ongoing efforts to improve sensitivity at lower power levels by pushing existing fabrication methods to make CRs smaller, such approaches are difficult and unlikely to provide revolutionary improvements [5][6][7]. Instead of using conventional fabrication methods to push CRs to smaller sizes, we have instead taken a different approach and designed a radiometer fabricated lithographically at the microscale level [8].…”