Fabry–Pérot open resonant cavities for measuring the dielectric parameters of mm-wave optical materials

Brodi D. Elwood; Paul K. Grimes; John Kovac; Miranda Eiben; Grant Meiners

doi:10.1117/12.3019149

1 November 2024 Fabry–Pérot open resonant cavities for measuring the dielectric parameters of mm-wave optical materials

Brodi D. Elwood, Paul K. Grimes, John Kovac, Miranda Eiben, Grant Meiners

Author Affiliations +

Proceedings Volume PC13102, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XII; PC1310220 (2024) https://doi.org/10.1117/12.3019149
Event: SPIE Astronomical Telescopes + Instrumentation, 2024, Yokohama, Japan

Conference Poster

Abstract

As millimeter-wave cosmology experiments refine their optical chains, precisely characterizing their optical materials under cryogenic conditions becomes increasingly important. For instance, as the aperture sizes and bandwidths of millimeter-wave receivers increase, the design of antireflection coatings becomes progressively more constrained by an accurate measure of material optical properties in order to achieve forecasted performance. Likewise, understanding dielectric and scattering losses is relevant to photon noise modeling in presently-deploying receivers such as BICEP Array and especially to future experiments such as CMB-S4. Additionally, the design of refractive elements such as lenses necessitates an accurate measure of the refractive index. High quality factor Fabry–Pérot open resonant cavities provide an elegant means for measuring these optical properties. Employing a hemispherical resonator that is compatible with a quick-turnaround 4 Kelvin cryostat, we can measure the dielectric and scattering losses of low-loss materials at both ambient and cryogenic temperatures. We review the design, characterization, and metrological applications of quasioptical cavities commissioned for measuring the dielectric materials in the BICEP3 (95 GHz) and BICEP Array mid-frequency (150 GHz) optics. We also discuss the efforts to improve the finesse of said cavities, for better resolution of degenerate higher order modes, which can provide stronger constraints on cavity parameters and sample material thickness.

Citation Download Citation

Brodi D. Elwood, Paul K. Grimes, John Kovac, Miranda Eiben, and Grant Meiners "Fabry–Pérot open resonant cavities for measuring the dielectric parameters of mm-wave optical materials", Proc. SPIE PC13102, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XII, PC1310220 (1 November 2024); https://doi.org/10.1117/12.3019149

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