A millimetre-wave superconducting hyper-spectral device
Résumé
Millimetre-wave observations represent an important tool for Cosmology studies. The Line Intensity Mapping (LIM) technique has been proposed to map in three dimensions the specific intensity due to line (e.g. [CII], CO) emission, for example from the primordial galaxies, as a function of redshift. Hyper-spectral integrated devices have the potential to replace the current Fourier transform, or the planned Fabry-Perot-based instruments operating at millimetre and sub-millimetre wavelengths. The aim is to perform hyper-spectral mapping, with a spectral resolution R = lambda / Delta_lambda = 100 - 1000, over large, i.e. thousands of beams, instantaneous patches of the Sky. The innovative integrated device that we have developed allows avoiding moving parts, complicated and/or dispersive optics or tunable filters to be operated at cryogenics temperatures. The prototype hyper-spectral focal plane is sensitive in the 80-90~GHz range and contains nineteen horns for sixteen spectral-imaging channels, each selecting a frequency band of about 0.1~GHz. A conical horn antenna, coupled to a planar superconducting filter, collects the radiation. A capacitively coupled Lumped Element Kinetic Inductance Detector (LEKID) is then in charge of dissipating and sensing the super-current established in the filter. The prototype is fabricated with only two photo-lithography steps over a commercial mono-crystalline sapphire substrate. It exhibits a spectral resolution R = 800. The optical noise equivalent power is in the observational relevant $10^{-17}~W/\sqrt{Hz}$ range. The device, as expected from 3-D simulations, is polarisation-sensitive, paving the way to spectro-polarimetry measurements over very large instantaneous field-of-views.
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