Demonstration of 220/280 GHz Multichroic Feedhorn-Coupled TES Polarimeter

Area of Science:

• Astrophysics
• Cosmology
• Instrumentation

Background:

• Cosmic Microwave Background (CMB) observations require sensitive polarimeters to study early universe physics.
• Previous Transition-Edge Sensor (TES) polarimeter designs covered frequencies up to 220 GHz.
• Extending detector frequency range is vital for comprehensive CMB analysis.

Purpose of the Study:

• To design and measure novel feedhorn-coupled TES polarimeters.
• To extend TES polarimetry to higher frequencies (220 GHz and 280 GHz).
• To evaluate the performance of new detector designs and compare power-termination schemes.

Main Methods:

• Fabrication of TES polarimeters with integrated orthomode transducers and diplexers.
• Utilized Fourier-transform spectroscopy for passband characterization.
• Employed a cryogenic thermal source for coupling efficiency measurements.
• Compared two distinct power-termination schemes for wide-bandwidth millimeter-wave polarimeters.

Main Results:

• Demonstrated TES polarimeter technology operating at frequencies up to 315 GHz.
• Achieved high optical efficiencies: 77% ± 6% at 220 GHz and 75% ± 5% at 280 GHz.
• Fourier-transform spectrometer measurements closely matched simulations.
• Identified no significant performance difference between tested power-termination schemes.

Conclusions:

• The developed TES polarimeters successfully extend high-frequency operation for CMB studies.
• The demonstrated optical efficiencies are competitive for sensitive cosmological measurements.
• The findings validate the detector design and provide insights into optimal power-termination strategies.