WSPEC: A waveguide filter-bank focal plane array spectrometer for millimeter wave astronomy and cosmology

TL;DR

WSPEC is a waveguide filter-bank spectrometer designed for millimeter wave astronomy, enabling large-scale spectral surveys with moderate resolution to study cosmic phenomena like large scale structure, star formation, and the SZ effect.

Contribution

The paper introduces WSPEC, a novel waveguide filter-bank spectrometer with integrated LEKID detectors, fabricated via metal machining, and demonstrates initial successful testing at multiple frequencies.

Findings

Successful initial testing of a WR10 prototype at 90 GHz.

Verification of the concept at higher frequencies with a WR5 prototype.

Design of a resonant backshort structure to improve optical efficiency.

Abstract

Imaging and spectroscopy at (sub-)millimeter wavelengths are key frontiers in astronomy and cosmology. Large area spectral surveys with moderate spectral resolution (R=50-200) will be used to characterize large scale structure and star formation through intensity mapping surveys in emission lines such as the CO rotational transitions. Such surveys will also be used to study the SZ effect, and will detect the emission lines and continuum spectrum of individual objects. WSPEC is an instrument proposed to target these science goals. It is a channelizing spectrometer realized in rectangular waveguide, fabricated using conventional high-precision metal machining. Each spectrometer is coupled to free space with a machined feed horn, and the devices are tiled into a 2D array to fill the focal plane of the telescope. The detectors will be aluminum Lumped-Element Kinetic Inductance Detectors (LEKIDs). To target the CO lines and SZ effect, we will have bands at 135-175 GHz and 190-250 GHz, each Nyquist-sampled at R~200 resolution. Here we discuss the instrument concept and design, and successful initial testing of a WR10 (i.e. 90 GHz) prototype spectrometer. We recently tested a WR5 (180 GHz) prototype to verify that the concept works at higher frequencies, and also designed a resonant backshort structure that may further increase the optical efficiency. We are making progress towards integrating a spectrometer with a LEKID array and deploying a prototype device to a telescope for first light.