Further optical analysis of the ALMA Band 9 front end for a possible upgrade

Sabrina Realini; Ronald Hesper; Andrey Baryshev; Jan Barkhof; Neil Phillips; Joost Adema

doi:10.1117/12.2629322

31 August 2022 Further optical analysis of the ALMA Band 9 front end for a possible upgrade

Sabrina Realini, Ronald Hesper, Andrey Baryshev, Jan Barkhof, Neil Phillips, Joost Adema

Proceedings Volume 12190, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XI; 121902Z (2022) https://doi.org/10.1117/12.2629322
Event: SPIE Astronomical Telescopes + Instrumentation, 2022, Montréal, Québec, Canada

Conference Poster

Abstract

The ALMA Band 9 (600–720 GHz) receiver is a dual channel heterodyne system capable of detecting orthogonally polarized signals using a wire grid. The light entering the front end is refocused with a compact arrangement of mirrors, which is fully contained within the cartridge. The cross–polar performance of existing Band 9 receivers does not meet the requirements specified for the ALMA channels, i.e. a cross-polar level lower than -23 dB. Moreover, this channel shows a relatively large beam squint, which makes this channel not suitable for extended-source polarimetry. Within the framework of ESO “Advanced Study for Upgrades of the Atacama Large Millimeter/sub-millimeter Array (ALMA)”, we analyze the possibility of improving cross-polarization performance by removing the grid and using an OMT to separate the two orthogonal polarizations. We set up the electromagnetic model of the optics to simulate its performance with and without the grid. The results of the simulations are compared with measurements. Another limiting factor for polarimetric observations in ALMA is the beam squint, which translates directly into a gradient of Stokes Q error across the field of view. The OMT-based ALMA bands show a beam squint within 2% of the FWHM, whereas band with wire grids show a much larger scatter. We investigate what causes the scatter in Band 9, trying to understand if it could be improved by reducing tolerances of the grid mounting or if it is a limiting factor related to aberrations in the current optics.

Conference Presentation

Citation Download Citation

Sabrina Realini, Ronald Hesper, Andrey Baryshev, Jan Barkhof, Neil Phillips, and Joost Adema "Further optical analysis of the ALMA Band 9 front end for a possible upgrade", Proc. SPIE 12190, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XI, 121902Z (31 August 2022); https://doi.org/10.1117/12.2629322

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available