# 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
It is proposed to have 1900, 950, and 475 pixels in its 1.1, 1.4, and 2.0 mm band respectively, and with two MKIDs per pixel (one per polarization direction) ToITEC will have 6650 MKIDs in total. MKIDs have also been an integral part in A-MKID [48; 49; 50], the APEX MKID camera, a project to build a large format, two band (850 \(\upmu\)m/353 GHz and 350 \(\upmu\)m/855 GHz) camera for the 12 m Apex (Atacama Pathfinder Experiment) telescope, Llano de Chajnantor Observatory, Chile. Efforts are also ongoing to build a 110 pixels, 90-110 GHz (3.3-2.7 mm) MKID camera for the 45 m telescope of Nobeyama Radio Observatory near Minamimaki, Japan. And there have been proposals published for the multicolor sub-THz KID-array camera MUSICAM [51], targeting four 25 pixel-arrays for 2.0, 1.33, 1.04, and 0.86 mm (150, 225, 288, and 350 GHz) and intended for the proposed Eurasian Sub-Millimeter Telescopes (ESMT) and for TeSIA [52], an MKID camera with 1024 pixels covering the 850 GHz (350 \(\upmu\)m) band for the proposed Date5 far-IR telescope on Dome A, Antarctica. A long-time goal for the MKID based on-chip filter-bank spectrometers (described in chapter 3.1.1) is to be combined into larger arrays to allow high resolution imaging spectroscopy of astronomical sources in the mm and sub-mm wavelength ranges. With between 50 and 500 individual MKIDs per pixel these arrays would have a very large detector count. A different approach to achieve at least medium energy resolution in this frequency range is to use a Martin-Puplett Interferometer (MPI) like the one suggested for the CONCERTO [53] instrument. CONCERTO, the CarbON CII line in post-rEionisation and ReionisaTiOn epoch instrument is a proposed MKID imaging spectrometer for the 12 m Apex telescope. CONCERTO intends to utilize two 2152 pixels MKID arrays similar to the NIKA-2 design to detect both polarizations of incoming light in the focal plane of its MPI. A Martin-Puplett Interferometer (MPI) is a Fourier transform spectrometer which resembles a Michelson interferometer with an oscillating mirror at the end of one arm and can deliver a differential spectrum with respect to a given reference. With an oscillation frequency of 4 Hz, CONCERTO expects to achieve a resolution of 1 GHz across its 130-310 GHz (2.3-0.97 mm) band for a spectral resolving power R between 130 and 300 [53]. KISS (the KIDs Interferometer Spectrum Survey) [54; 55] is a pathfinder instrument for CONCERTO and has recently been commissioned to the 2.25 m QUIJOTE telescope of Teide Observatory, Tenerife. KISS uses two 316 pixels arrays with MKIDs made from Ti/Al bilayers, observes in the 80-300 GHz (3.7-1.0 mm) band and has an MPI with a mirror path length of 10 cm and mirror oscillation frequency of 5 Hz. It reaches 1 GHz frequency resolution and is mainly dedicated (like CONCERTO) to observe galaxy clusters by studying secondary anisotropies of the Cosmic Microwave Background (CMB). In the far-IR to microwave region of the electromagnetic spectrum Earth's atmosphere absorbs most of the incoming light. Many astronomical observations can therefore only be performed from space with telescopes on satellites. There are several projects to adapt MKIDs to be used as far-IR to microwave detectors for in-space applications. The SPACEKIDs collaboration [56; 57; 58; 59] aimed to investigate the general suitability of MKIDs for far-IR to sub-mm space applications and demonstrated among others a 961 pixels MKID array centered around 850 GHz (350 \(\upmu\)m) with competitive noise levels and cosmic -ray dead times. MKIDs made from Al and NbTiN have been suggested [60; 61] for the far-IR (34-210 \(\upmu\)m) spectrometer SAFARI on the proposed 2.5 m SPICA (Space Infrared telescope for Cosmology and Astrophysics) infrared space telescope, and prototype arrays of 989 membrane-suspended MKIDs for the 1.4-2.8 THz (214-107 \(\upmu\)m) band have been demonstrated [58]. MKIDs are also being considered for CORE [62], the Cosmic ORigins Explorer, a space telescope to observe the CMB polarization.