The cosmic microwave background (CMB) provides a powerful tool for probing the earliest moments of the universe. However, millimeter-wave observations are complicated by the presence of astrophysical foregrounds, such as synchrotron emission and galactic dust, which also radiate at these wavelengths. By designing detectors with broad spectral coverage, these foregrounds can be separated from the CMB because their spectral energy distributions are distinct. For this reason, we are developing feedhorn-coupled transition-edge-sensor (TES) polarimeters with two passbands centered at 220 GHz and 280 GHz. Each pixel couples polarized light to two linear polarizations using a planar orthomode transducer (OMT) and senses the power via four TES bolometers, one for each band in each linear polarization. Extending our OMT-coupled design to higher frequencies is necessary for foreground rejection. However, this is challenging due to greater microwave loss at these frequencies and smaller dimensions, which require tighter tolerances. We describe the device design and show the simulated performance of all microwave components in the detection chain, highlighting the OMT and diplexer. Furthermore, we present measurement results of these devices, including passbands, polarization response, beam shape, and optical efficiency. Lastly, we comment on the implementation of this design for arrays soon to be fielded in ground-based instruments for the Simons Observatory.
Acknowledgments: This work was supported in part by the NASA APRA program, grant #NNX17AL23G. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1144083.
|Less than 5 years of experience since completion of Ph.D||Y|
|Student (Ph.D., M.Sc. or B.Sc.)||Y|