# Applications for Microwave Kinetic Induction Detectors in Advanced Instrumentation
## 3 MKID Applications in Observational Astronomy
### Observational Astronomy: Infrared to Microwaves
#### 3.1.2 MKID Mid-IR to Microwave Imagers
CORE is proposed to cover 60-600 GHz (5-0.5 mm) in 19 bands with a 1.2 m telescope and 2100 pixels. For the Origins Space Telescope (OST) a concept for highly sensitive Al MKIDs that would be capable to count single mid-IR photons has been proposed [63; 64]. OST is a mid-IR to far-IR telescope concept with a 6-9 m aperture and a targeted sensitivity band of 6-40 \(\upmu\)m (50-7.5 THz). The JAXA (Japan Aerospace Exploration Agency) satellite for CMB observations LiteBIRD also initially considered MKIDs for its main instrument [65; 66]. MKID development work is ongoing for GEP, the Galaxy Evolution Probe and its pathfinder balloon-born mission GEP-B [67]. GEP is a concept for an in-space observatory to study mid- and far-IR spectra of galaxies, designed with large arrays with more than 25,000 detectors. MKIDs for GEP should be able to cover 10-400 \(\upmu\)m (30-0.75 THz), and especially in the 10-100 \(\upmu\)m range few MKID designs have so far been demonstrated. Compared to satellites, high altitude balloons offer an easier and less cost intensive alternative to place a telescope above most of Earth's atmosphere. BLAST-TNG [68; 69; 70], the next generation upgrade for the 'Balloon-borne Large Aperture Submillimeter Telescope' is using a 2.5 m telescope on a balloon to study the role magnetic fields play in star formation by observing polarized light from the interstellar medium in three bands centered around 250, 350, and 500 \(\upmu\)m (1200, 857, and 600 GHz). For this BLAST-TNG uses MKIDs made from TiN in large arrays of 1836, 938, and 544 detectors for the 250, 350, and 500 \(\upmu\)m bands respectively. A single BLAST-TNG pixel has two MKIDs, one for each polarization, with their inductors at 90 degrees to each other to act as polarization sensitive antennas. Observing at longer wavelengths is OLIMPO (the Osservatorio nel Lontano Infrarosso e le Microonde su Pallone Orientabile) [71; 72; 73; 74], a 2.6 m MKID telescope on a balloon that can reach altitudes up to 38 km. It is optimized to study galaxy clusters and observes in four bands around 150, 250, 350, and 460 GHz (2.0, 1.2, 0.86, and 0.65 mm). Its MKIDs are made from aluminum, it has between 19 and 41 pixels per band and it uses an MKID design similar to NIKA with a fractal inductor as sensitive antenna for all polarizations. OLIMPO has concluded its first observation campaign in 2018 after being launched from Longyearbyen, Svalbard and circling the North Pole. This flight was the first time MKIDs have been used for not-ground-based observations and was able to prove [72; 74] that MKIDs are capable to withstand the demanding conditions on high altitude balloons. MKIDs made from Al have also been part of the proposal for SKIP (Strataspheric Kinetic Inductance Polarimeter) [75], a balloon-born 0.5 m telescope to observe the cosmic microwave and infrared backgrounds. SKIP intended to have 2317 single-polarization MKIDs and be capable to observe in a band either around 150 GHz (2.0 mm) or between 260 and 350 GHZ (1.2-0.9 mm), depending on installed filters. Finally, MKIDs are also intended to be used with B-SIDE [76], a further proposed, 0.8 m aperture balloon-born instrument to observe polarized emission between 400 and 700 GHz (750 and 430 \(\upmu\)m) with 980 to 1800 pixels, meant to improve foreground subtraction for CMB B-mode observations. Ground-based observations of the Cosmic Microwave Background (CMB) have been a significant driving force behind the development of low temperature detectors for many years. Especially the observation of the so-called B-mode polarization of the CMB is attracting tremendous scientific interest as it could provide evidence for cosmic inflation shortly after the Big Bang. There are multiple CMB B-mode experiments ongoing and in late planning phases at the moment, and MKIDs are considered for several of them and already utilized in some.