UCL Astrophysics Group


Polarisation Modulators

Our research involves the design and modelling of current state-of-the-art modulators.

Cosmological and Astrophysical experiments rely on the detection and quantification of photons with different wavelengths. Much information can also be retrieved  with the knowledge of the polarisation nature of the detected light. In cosmology, the cosmic microwave background is partially polarised (less than ten percent). From the distribution of the polarisation fraction of this relic signal in the sky we can constrain modern cosmological theories and observe the footprint of gravitational waves originated during inflation.

In submm astrophysics the percentage of polarised radiation is directly linked to the presence of local magnetic fields which align the particles of  light emitting dust. In order to detect this polarised fraction of light in any instrument it is necessary to separate it optically from the unpolarised component. This can be achieved with a number of different polarisation modulators.  Our research involves the design and modelling of current state-of-the-art  modulators such as achromatic crystal Half-Wave plates, as well as studying new technologies for future modulators such as engineered artificial  birefringence in plastic materials and metal meshes.

A list of current and future experiments with our involvement in the design or construction of polarisation modulators are:

Cosmology: EBEX, Polarbear, CLOVER
Astrophysics: BlastPol, Pilot, MKID-Pol, SCUBA2

Polarisation systematics:

Polarisation graph
Every optical component in the path of photons entering an optical system requires accurate modelling.  This allows a systems' performance to be predicted. Comparing experimental data with predictions allow us to verify and improve our knowledge of defects in the optics and their behaviour as a function of parameters such as temperature and mechanical stress.  Current studies include the polarised optical performance of anti-reflection coatings  on large lenses for space satellite missions and the thermal efficiency of  spectral band defining spectral filters.