Modelling the Partially Coherent Behaviour of Few-Mode Far-Infrared Grating Spectrometers

TL;DR

This paper introduces a modal technique for accurately modelling ultra-low-noise far-infrared spectrometers, accounting for partial coherence, few-mode responses, and straylight, aiding the design of next-generation space observatories.

Contribution

A novel modal modelling approach that handles partially coherent fields and straylight in few-mode far-infrared spectrometers, improving upon conventional methods.

Findings

Successfully models the SAFARI instrument's behaviour

Accounts for straylight radiated by warm internal surfaces

Demonstrates applicability to space observatory spectrometers

Abstract

Modelling ultra-low-noise far-infrared grating spectrometers has become crucial for the next generation of far-infrared space observatories. Conventional techniques are awkward to apply because of the partially coherent form of the incident spectral field, and the few-mode response of the optics and detectors. We present a modal technique for modelling the behaviour of spectrometers, which allows for the propagation and detection of partially coherent fields, and the inclusion of straylight radiated by warm internal surfaces. We illustrate the technique by modelling the behaviour of the Long Wavelength Band of the proposed SAFARI instrument on the well-studied SPICA mission.