The nursery is stellar. Credit: NASA/JPL-Caltech.
The work horses of supra-terahertz astronomy are the receivers that combine a hot electron bolometer with a reference oscillator. Niobium nitride HEBs have been used for space and balloon-borne telescopes. A team of scientists at SRON, TU Delft, and RUG have demonstrated a HEB based on magnesium diboride, a new material that can detect more lines and operate at 20 kelvin. The latter can reduce the cost, weight, volume, and electrical power of space instruments. The study was published.
The most sensitive HEBs are superconducting niobium nitride. They use a local oscillator to convert a THz line into a GHz line. Information about star formation in the galaxies is provided by many atomic, ionic, and molecular lines.
The SOFIA airborne telescope, the STO2 balloon telescope, and the Herschel Space Observatory have all been successfully applied with the Heterodyne mixers. They will fly on NASA's GUSTO balloon telescope, which will be launched in the end of 2022, and be selected as detectors for the proposed OASIS space mission. The earth's atmosphere blocks the supra-terahertz frequencies from being accessible for ground-based telescopes.
Superconducting.
HEBs have a limited intermediate Frequency bandwidth, which covers a limited line in one measurement. The low operating temperature of around 4 Kelvin is a restriction due to their low critical temperature. The constraints on mass, volume, electrical power and cost make cooling down to 4 Kelvin impractical for a space observatory.
A group of scientists at SRON, RUG, and other institutions have recently demonstrated a HEB based on a new material of magnesium diboride. The first low-noise performance of a detector at an operating temperature of 20 Kelvin has been shown by two people.
The NbN HEB's bandwidth is three times larger than the large IF bandwidth measured by Gan. The larger bandwidth can cover more lines within a single measurement. The thin film has a critical temperature of 38.6 kelvin.
The operating temperature is higher.
The higher operating temperature of 20 Kelvin is attractive for space applications because of the compact, low-mass, low-dissipation, and space qualified Stirling coolers. The latter can reduce the cost of space instruments. The new detectors can increase the opportunities for new space instruments and telescopes, such as an M-class far-infrared space mission recommended in the next generation of THz observatories and a number of telescopes operated as interferometers in space.
The low noise MgB2 hot electron bolometer mixer operated at 5.3 THz and at 20 K was described in the article. It's called 10.1063/5.0070153.
The Applied Physics Letters is a journal.
Bolometers operate at higher temperatures using a new material.
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