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INTRAPIX - A one-of-a kind characterization device

Researchers from the Low Temperature Systems Department of our institute have developed a unique test bench that will allow the intra-pixel characterization of matrix detectors, for visible or infrared in astrophysics.

Published on 30 August 2019
In order to observe ever further with better resolution the stars and galaxies, highly sophisticated devices are designed. Thus, the performance of the sensors and their capability to detect the faintest signals are significantly improving over time. This is the case for the bolometer, a thermal detector whose general principle is to convert the energy of an incident radiation into heat which then raises the temperature of an absorber featuring a thermometer. Each detector has a few thousand pixels, each representing a square of about ten µm side. However, when a photon reaches a pixel, it seems that it would generate a different signal depending on the point of impact, edge or center of the pixel. Hence the Intrapix project is a cryostat designed to accurately characterize these bolometers.

The Low Temperature Systems Department (D-SBT) at IRIG institute has established itself over time as a reference within the space cryogenics community. As part of the Herschel mission, the largest telescope ever placed in orbit, D-SBT designed the cryorefrigerators to cool the observation detectors of two instruments to about 300mK. ArTeMis, a sub-millimeter photonic camera operated by CEA-Saclay's Institute of research into the fundamental laws of the Universe (IRFU), has benefited from the Herschel legacy. Indeed, this camera composed of bolometers operating at 300 mK and installed at the focus of the large Apex telescope (Chile) is cooled by a cryogenic chain and a cryostat entirely designed by D-SBT.
It is therefore natural that IRFU turns to D-SBT to contribute to the Intrapix project, with the dual objective of designing an optical test bench to characterize these bolometers and developing a brand new cryostat to maintain this bench at low temperature. This cryostat includes a cryogenic part featuring a liquid nitrogen tank and a pulse tube for cooling the bench and the detectors. During the design phase, pre-dimensioning calculations (without optics) carried out by D-SBT showed that no thermomechanical stress could generate significant deformations that could affect the path of the light beam (Figure). A special cryogenic heat treatment of the bench will be carried out to guarantee its dimensional stability over time..
The integration of the optical bench in the cryostat (Figure), with these different optical components, will allow the Intrapix project to serve the largest European astrophysics projects such as Euclid-VIS, JWST-Miri, PLATO. Intrapix is unique in the world and will allow the intra-pixel characterization of matrix detectors, for visible or infrared in the field of astrophysics.

Intrapix operating diagram.
Cross section showing the inside of the cryostat designed and made by D-SBT. The optical test bench features various components (mirrors, filter wheel, collimators, pattern test pattern, etc.) designed by the IRFU Astrophysics Department and made by Durham University.
In yellow: path of the light beam.

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