Proof of concept
To establish a proof of concept and validate the observational strategy that underlies the COSMOCal project, we designed and assembled a prototype instrument designed to operate within the atmospheric window centered at 260 GHz. The first image on left details the main componentes:
A radio frequency chain that generates a monochromatic signal at 260 GHz and directs it through a waveguide to a conical horn. The electronic chain design is based on that of the 300 GHz channel of the space-qualified JUICE-SWI instrument developed at the Observatoire de Paris-PSL / LERMA.
A metal grid polarizer that ensures the purity of the polarized signal.
An optical laser to illuminate the grid polarizer generating a diffraction pattern, enabling to recover and monitor the alignment of the wires, and thereby the orientation of the signal polarization output.
Optics to focus the image of the diffraction pattern onto a CDD camera with a flip mirror to alternatively image ground landmarks onto the CCD camera to determine the 3D position and orientation of the COSMOCal source by photogrammetry.
In-lab characterization and first campaign
Ritacco et al (2024) provides a detailed presentation of this prototype instrument and its laboratory characterization at LPSC in Grenoble in February 2024, which showed a precision on the knowledge of the output polarization angle of <0.08 degrees. End of September 2024, we carried out a first campaign of tests at the IRAM 30m with the NIKA2 camera. The prototype source was installed on Pico Veleta a few km from the telescope. The measurements were successful and the data are being analyzed.
Laboratory tests at LPSC Feb. 2024
Tests campaign at the IRAM 30m telescope, Oct. 2024