Modeling sidelobe response for ground-based mm-wavelength telescopes with the geometrical theory of diffraction

TL;DR

This paper enhances optical modeling of ground-based mm-wavelength telescopes by integrating diffraction effects using GTD, improving the understanding of sidelobe responses crucial for CMB experiments.

Contribution

It introduces the application of the Geometrical Theory of Diffraction (GTD) to model sidelobe responses in telescope designs, addressing limitations of Geometrical Optics.

Findings

GTD effectively models diffraction-induced sidelobes.

Simulation results inform optimal forebaffle design.

Ground screen interactions significantly influence sidelobe patterns.

Abstract

Accurate optical modeling is important for the design and characterisation of current and next-generation experiments studying the Cosmic Microwave Background (CMB). Geometrical Optics (GO) cannot model diffractive effects. In this work, we discuss two methods that incorporate diffraction, Physical Optics (PO) and the Geometrical Theory of Diffraction (GTD). We simulate the optical response of a ground-based two-lens refractor design shielded by a ground screen with time-reversed simulations. In particular, we use GTD to determine the interplay between the design of the refractor's forebaffle and the sidelobes caused by interaction with the ground screen.