Far-Infrared double-Fourier interferometers and their spectral sensitivity

TL;DR

This paper explores the design and noise considerations of double-Fourier interferometers for far-infrared astronomy, focusing on their spectral sensitivity and application in balloon-based telescopes like BETTII.

Contribution

It analyzes the impact of noise on spectral sensitivity and discusses the unique characteristics of space- and balloon-based double-Fourier interferometers, with application to BETTII.

Findings

Intensity and optical path difference noise affect spectral signal-to-noise ratio.

Single-baseline interferometers have specific characteristics for wide-field imaging.

Application to BETTII demonstrates feasibility of far-infrared interferometry on a balloon platform.

Abstract

Double-Fourier interferometry is the most viable path to sub-arcsecond spatial resolution for future astronomical instruments that will observe the universe at far-infrared wavelengths. The double transform spatio-spectral interferometry couples pupil plane beam combination with detector arrays to enable imaging spectroscopy of wide fields, that will be key to accomplishing top-level science goals. The wide field of view and the necessity for these instruments to fly above the opaque atmosphere create unique characteristics and requirements compared to instruments on ground-based telescopes. In this paper, we discuss some characteristics of single-baseline spatio-spectral interferometers. We investigate the impact of intensity and optical path difference noise on the interferogram and the spectral signal-to-noise ratio. We apply our findings to the special case of the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII), a balloon payload that will be a first application of this technique at far-infrared wavelengths on a flying platform.