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William Herschel Telescope

ExPo: Extreme Polarimeter

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.


Publications: research or technical papers, etc.

Instrument information:

Rodenhuis, M.; Canovas, H.; Jeffers, S. V.; Keller, C. U., 2008, "The Extreme Polarimeter (ExPo): design of a sensitive imaging polarimeter", SPIE Proc., 7014, 70146T.

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Last modified: 27 April 2018