The KID far infrared detector achieves the highest possible sensitivity

The KID far infrared detector achieves the highest possible sensitivity

The KID far infrared detector achieves the highest possible sensitivity

Andromeda galaxy in the far infrared. Credit: ESA/NASA/JPL-Caltech/B. Schulz

Astronomy has a blind spot in far infrared radiation compared to most other wavelengths. A far infrared space telescope can only use its full sensitivity with an actively cooled mirror at temperatures below 4 Kelvin (-269℃). Such a telescope does not yet exist, which is why there has been little global investment in the development of corresponding detectors.

In 2004, SRON decided to break this cycle and invest in the development of Kinetic Inductance Detectors (KIDs). Now researchers from SRON and TU Delft have achieved the highest possible sensitivity, comparable to feeling the heat of a candle on the moon from Earth. Their study appears in Astronomy & Astrophysics September 6.

In recent years, we have been spoiled with the most beautiful images from telescopes operating with X-rays, infrared, radio and visible light. To name a few: the image of the black hole in M87, the Hubble Extreme Deep Field or the baby image of a planetary system. But in a wavelength range, astronomy is relatively blind: the far infrared, especially at wavelengths between 300 μm and 10 μm.

Earth’s atmosphere blocks most of this radiation for ground-based telescopes, while space telescopes are often so hot that they blind their detectors with the far-infrared radiation they themselves emit. With so much noise, there is little incentive to spend large sums of money on the development of more sensitive far infrared detectors. And with a lack of sensitive detectors, governments won’t allocate funds to supercooled silent telescopes.


At the beginning of this century, SRON decided to break the pattern and invest in the development of Kinetic Inductance Detectors (KIDs). This decision is now bearing fruit. Together with TU Delft, SRON researchers have almost perfected the technology by making it sensitive enough to see the permanent background radiation of the universe.

“An even higher sensitivity would be of no use,” says Jochem Baselmans (SRON/TU Delft). “Because you will always be limited by the noise of the background radiation from the universe. So our technology provides telescope builders like NASA and ESA with far-infrared detectors that are as sensitive as possible. We are already seeing two proposals submitted to NASA for a super-cooled telescope. These are much more expensive than relatively hot telescopes, but our KIDs are worth it.”

Terahertz deviation

KIDs help astronomy bridge the terahertz gap, named after the frequency of far infrared light. Astronomers are now missing the light produced by stars in the distant, young universe, leaving a void in our knowledge of stellar evolution. Additionally, the terahertz gap is a unique opportunity for adventurous astronomers to dive into the unknown.

“You don’t know what you don’t know. The Hubble Deep Field was created by pointing the Hubble Telescope at a pitch-black piece of sky with seemingly nothing in it. Subsequently, thousands of galaxies emerged , of a smaller area less than one percent of the full moon,” says Baselmans.

The sensitivity the researchers achieved with their KIDs can best be described by a hypothetical candle on the moon. Imagine standing on Earth – or floating just above the atmosphere – and raising your hand to feel the warmth of the candle. Does this seem like a futile exercise to you? Not for a CHILD. It’s even ten times more sensitive than that. With an integration time of one second, a KID can detect as few as 3*10-20 watt.

Promising far-infrared detectors better protected against cosmic rays

More information:
JJA Baselmans et al, Super-THz ultra-sensitive microwave kinetic inductance detectors for future space telescopes, Astronomy & Astrophysics (2022).

Provided by SRON Netherlands Institute for Space Research

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