CfCP involvement in EDGE

The CfCP is mainly responsible for building the detectors and determining their intrinsic properties before they are installed on the telescope. The goal of the detector development is to verify the optical efficiency and detector noise properties of the bolometers over the necessary range of detector wavelengths. There are two efforts currently underway:

• The design and characterization of the optical properties of the bolometer elements
• The design of the readout electronics for the Transition Edge Sensor (TES) elements

The optical properties are modeled numerically and the design optimized. Our collaborators at Goddard Space Flight Center (GSFC) then manufacture optical test devices. At Chicago we then test these devices optically with our Fourier Transform Spectrometer (FTS) and compare the models with the experimental properties. Currently we are refining the models to increase their fidelity and usefulness for predicting the absorption spectrum.

The testing of the bolometers is being carried out in the cryostat shown in the following image (a cryostat is a sophisticated refrigerator that cools to very low temperatures). This cryostat and setup is not part of the final EDGE flight(s). It is for testing prototypes of the detectors that will eventually be used in the EDGE mission.

 
This is the cryostat that will cool bolometers (infra-red radiation detectors) to below 0.3 K. The bolometers will be mounted on the L-shaped copper piece (indicated by the black arrow) which lies along the optical axis of the cryostat. (The optical axis is the imaginary horizontal line that runs parallel to and through the "center" of the L shaped copper piece.) The "top lid" of the cryostat, which will cover this whole setup, has a small window which lets radiation shine through the stack of frequency-selective bolometers mounted to the L-bracket. The L-bracket and everything on it will be cooled through the thermal straps (the thin metal pipes) that go between it and the ultra-cold parts of the cryostat (the gold-colored disks close to the bottom). The metallic sheets surrounding the innards of the cryostat reflect away thermal radiation (from the walls of the cryostat, not the external radiation we want to measure) that may otherwise warm up the insides. The bolometers must be cooled to such low temperatures to obtain the requisite sensitivity. This cryostat and setup is not part of the final EDGE flight(s). It is for testing prototypes of the detectors that will eventually be used in the EDGE mission.