Title: A 25-micrometer Single-Photon-Sensitive Kinetic Inductance Detector
Authors: Peter K. Day, Nicholas F. Cothard, Christopher Albert, et al.
First Author’s Institution: Jet Propulsion Laboratory, California Institute of Technology
Status: Published in PRX [open access]
Observations of infrared (IR) through millimeter (mm)-wavelength light have great promise for facilitating breakthroughs in the fields of exoplanet spectroscopy, planet formation, galaxy evolution, and cosmology. However, building detectors to make these observations is challenging. For example, measuring the faint signal of an exoplanet requires a detector that can remain stable over many hours of operation, while cosmological measurements require extremely sensitive detectors with a large dynamic range to detect sources with various intensities.
KIDs Being KIDs
Cryogenic detectors are typically the preferred technology for such observations. Kinetic inductance detectors, or KIDs, are one type of these detectors. KIDs are made of superconducting materials which contain pairs of weakly-bound electrons called Cooper pairs. The inductance of a superconductor is inversely proportional to the Cooper pair density, which means that when a photon strikes a superconductor, it breaks these Cooper pairs, thus increasing the inductance. In a KID, this inductance is combined with a capacitor to create a resonant circuit with a characteristic frequency. When a photon hits a KID, this frequency shifts. If the circuit is excited by a probe signal tuned near the resonant frequency, an incident photon will be seen as a change in the phase and amplitude of the probe signal.
A New KID on the Block
The authors of today’s paper share the performance of an array of new KIDs designed to detect a mid-IR wavelength of 25 microns. The array, shown in Figure 1, contains 44 KIDs arranged in two rows with an array of lenslets to focus photons onto each KID. The KIDs consist of a meandering strip of aluminum, which is superconducting at temperatures below 1.2 K, coupled to a pair of niobium capacitors. The pattern of the aluminum strip enables the KIDs to selectively absorb photons with wavelengths around 25 microns. This pattern can be modified to make detectors sensitive to other wavelengths.
To demonstrate the capabilities of these detectors, the authors cooled them to 150 mK and measured their response to a blackbody source in a variety of tests. In one test, they varied the blackbody source temperature from 3 to 42 K to simulate the faint light expected from an exoplanet. Because the wavelength of photons able to reach the detectors is in the tail of the blackbody emission spectrum, only a few photons per second will be detected. For higher blackbody temperatures, the amplitude of the spectrum’s tail increases. This suggests that photons should reach the detectors at a higher rate for higher blackbody temperatures, which is exactly what the authors observed (Figure 2). In another test, they modulated the blackbody temperature between 100 and 100.01 K over a 6-hour period (Figure 3). They found that the detectors were sensitive enough to register this small temperature variation, and their response remained stable during the test.
The authors have shown that these new KIDs are versatile detectors that can stably measure sources with a wide range of intensities. They have the potential to enable state-of-the-art measurements and make advances in various fields of astrophysics and cosmology.
Astrobite edited by Caroline von Resfeld
Featured image credit: Adapted from NASA/European Space Agency/Space Telescope Science Institute/J. de Wit (MIT) and Figure 1 of today’s paper.
Discover more from astrobites
Subscribe to get the latest posts to your email.
