A Cosmic Microwave Background Polarimeter
Project website: External pages
The CMB group at the IAC (http://www.iac.es/project/cmb ) , in collaboration with the University of Santa Barbara (UCSB), have developed a method of measuring microwave polarisation using a large number of low-cost radio-telescopes situated in several high quality observatories around the world. The resulting observations are of a high quality and, through the combination of simultaneous measurements, highly sensitive.
The main objective is to almost completely cover the entire sky, allowing for highly sensitive measurements of B-modes at low multipoles, l . Given that the radiometers will be basically independent of each other (i.e. not in the same observatory) the ground-based systematic effects, like atmosphere, horizon, interference etc can be eliminated. This concept is different from other experiments, which have opted to place large ( >100) arrays of radiometers in the focal plane of one telescope. In this scenario systematic elimination and control is more difficult.
Each telescope in the IAC/UCSB design will sport a group of HEMT based radiometers. Each radiometer, as in the standard correlator design, is able to measure the Stokes parameters - U and V - simultaneously. However, the new IAC/UCSB design differs from conventional microwave polarimeters in that the polar signal is derived from an optical polar modulator. This type of polarimeter is new to microwave polarimetry and is normally found at optical wavelengths (more commonly known as a (half-wave plate). The transfer to microwave frequencies brings limitations e.g bandwidth < 20% and loss 0.1dB. These limitations are not of so much concern at optical frequencies.
The scientific goals for the prototype are
Principal Investigator: Rafael Rebolo