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William Herschel Telescope

The Extreme Polarimeter (ExPo)

First light: 9 October, 2008.


Designed and built by: ExPo was developed at the Astronomical Institute of Utrecht University.

Description: The Extreme Polarimeter (ExPo) aims to study circumstellar material at a contrast ratio with the central star of 10-9. Working at visible wavelengths, it will provide an inner working angle down to 0.5 arcsec and a field of view of 20 arcsec diameter. ExPo employs a dual beam-exchange technique based on polarimeter designs for solar studies. A partially transmitting coronagraph mask placed in the first focus reduces the light of the star. The beam is modulated using three ferro-electric liquid crystals in a Pancharatnam configuration, then split in a polarizing beamsplitter. Both beams are re-imaged onto the same Electron-Multiplying CCD camera.


More information:

More photos of this instrument: http://www.ing.iac.es/PR/archive/wht/instruments.html

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Last modified: 23 July 2015