Fast far-sidelobe modeling for centimeter to sub-millimeter astrophysical observations

Abstract

Next-generation centimeter to sub-millimeter telescopes require exquisite control over instrumental far-sidelobe response to accurately measure faint signals like the Cosmic Microwave Background B modes. Because existing electromagnetic modeling methods are computationally expensive, we developed a novel, diffraction-based beam modeling method for rapid and low-cost calculations. We applied this methodology to model the BICEP3 far-sidelobes and found good qualitative agreement with in situ beam measurements. Using this validated simulated beam, we calculated the sidelobe temperature pickup for a specific observation scenario: scanning near the slopes of Cerro Toco in the Atacama Desert. This rapid, predictive framework is most valuable as a tool for optimizing instrument baffling and identifying efficient scan strategies during the conceptual design phase.

Figures (7)

• Figure 1: Diagram of optical configuration used in this study with key parameters labeled, as listed in Table \ref{['tab:optical_params']}.
• Figure 2: Peak normalized beam intensity at the sky-side of the baffle for edge (Left) and center (Right) pixels at 96 GHz.
• Figure 3: Peak normalized beam intensity in the far-field center (Right) pixels at 96 GHz, projected onto (latitude, longitude) = (70$^{\circ}$, -110$^{\circ}$).
• Figure 4: Band- and azimuthally-averaged beam profile of a BICEP3-like telescope, showing focal-plane averaged (black) beam, center (red) pixel beam, and edge (blue) pixel beam.
• Figure 5: Band- and azimuthally-averaged beam profile of a BICEP3-like telescope, showing focal-plane averaged beam from simulations (black) and measurements by Giannakopoulos et al (teal).