Fermilab is currently assembling components required to perform optical tests with the Large Aperture Telescope mid-frequency (LAT-MF) detector wafers.
Fig. 1, below, shows the Fermilab dilution refrigerator being prepared for testing detector modules. 100 mK electronics circuits have been installed recently, and Fermilab scientists are now preparing the choke, waveguide interface plate, and backshort wafers.
These precision etched wafers hold the superconducting detector wafers in place and form a precisely shaped optical cavity for detecting the CMB microwave signal. Fig. 2, below, shows a recently completed precision-etched LAT-MF waveguide interface plate made out of Cu coated silicon. Radiation is coupled to the detector wafers through feedhorn arrays which are precision-machined to specific requirements of the telescope and its frequency band.
Fig. 3, below, shows a recently completed LAT-MF feedhorn array after inspection at Fermilab and the final gold-plating step. In addition, Fermilab’s engineering team has developed a novel feedhorn array configuration for the Small Aperture Telescopes (SAT).
That design incorporates sloped sidewall corners to enable a tighter module packing for the curved SAT focal plane. Fig. 4, below, shows a newly developed compact feedhorn array design for the SAT curved focal plane.
Originally posted in the CMB-S4 March 2023 Newsletter