KEYWORDS: Telescopes, Control systems, Polarimetry, Control systems design, Software development, Interfaces, Human-machine interfaces, Telecommunications, Optical instrument design, Data communications
The ASTE Polarimeter (APol), developed by Dr. Li at the Chinese University of Hong Kong (CUHK), presented a simple but innovative approach to carry out polarimetric measurements using ASTE Telescope’s TES camera. Our group at Universidad Austral de Chile (UACh) has collaborated in the project since its early stages and was assigned with the task of developing the control software for the instrument. The software has been developed also keeping the simplicity concept in mind. All its functionality has been separated in simple modules which are in charge of well defined tasks. The interfaces between the modules follow the design of modern applications and are based on well defined standards, such as those used by internet applications. The instrument has also the opportunity to be tested on the JCMT Telescope, and it is going to be used as the base design for a polarimeter in the future Leighton Chajnantor Telescope (LCT). Therefore, there is a requirement that the control software should be flexible enough to interface with at least these three telescopes, all of which run very different control software systems. This paper presents the design and implementation of APol’s control software, as well as some results of laboratory tests of the instrument.
The Atacama Submillimeter Telescope Experiment (ASTE) 10m aperture telescope has a multicolor camera based on a spiderweb absorber Transition Edge Sensor (TES) bolometer array. We developed a fore-optics module – ‘APol’, to convert 256 pixels of the TES camera into a sensitive imaging polarimeter at 350 ± 25 GHz. We used the simple half-wave plate - wire grid - camera design in APol, and it can cover 7’.5 FOV of ASTE. Here we describe the detailed optical design of APol and present result of the preliminary test carried out with the same optical system and camera at National Astronomical Observatory of Japan (NAOJ) laboratory.
SHARC-II is a 32 × 12 pixel submillimeter camera that is used with the ten-meter diameter Caltech Submillimeter
Observatory (CSO) on Mauna Kea. This camera can be operated at either 350 or 450 microns. We developed a module
that is installed at the CSO Nasmyth focus in order to convert SHARC-II into a sensitive imaging polarimeter, which we
refer to as "SHARP". SHARP splits the incident beam into two orthogonal polarized beams that are then re-imaged onto
different halves of the SHARC-II bolometer array. When this removable polarimetry module is in use, SHARC-II
becomes a dual-beam 12 × 12 pixel polarimeter. Sky noise is a significant source of error for submillimeter continuum
observations. Because SHARP will simultaneously observe two orthogonal polarization components, we are able to
eliminate or greatly reduce this source of error. Here we describe the design of SHARP and report preliminary results of
tests and observations carried out during our first two runs at CSO in August 2005 and January 2006.
The Submillimeter High Angular Resolution Camera II (SHARC-II) is a 32 x 12 pixel submillimeter camera that is used with the ten-meter diameter Caltech Submillimeter Observatory (CSO) on Mauna Kea. SHARC-II can be operated at either 350 or 450 microns. We are developing an optics module that we will install at a position between the SHARC-II camera and the focus of the CSO's secondary mirror. With our module installed, SHARC-II will be converted into a sensitive imaging polarimeter. The basic idea is that the module will split the incident beam coming from the secondary into two orthogonally polarized beams which are then re-imaged onto opposite ends of the “long and skinny” SHARC-II bolometer array. When this removable polarimetry module is in use, SHARC-II becomes a dual-polarization 12 x 12 pixel polarimeter. (The central 12 x 8 pixels of the SHARC-II array will remain unused.) Sky noise is a significant source of error for submillimeter continuum observations. Because our polarimetry module will allow simultaneous observation of two orthogonal polarization components, we will be able to eliminate or greatly reduce this source of error. Our optical design will include a rotating half-wave plate as well as a cold load to terminate the unused polarization components.
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