Development of metamaterial lenslet arrays for Cosmic Microwave Background experiments.

Measurements of the polarisation states of the Cosmic Microwave Background (CMB) radiation is currently one of the hottest topics in Cosmology. In particular, the detection of the associated primordial B-modes is the present challenge in this field. The Astronomy Instrumentation Group, within the School of Physics and Astronomy, is involved in many projects world-wide targeting the detection of the B-modes.
The B-mode signals are extremely weak and require instrumentation with extraordinary sensitivity and exquisite control of the optical systematic effects. High sensitivity can be achieved by using thousands of detectors coupled to very compact arrays of pixels/antennas. Current solutions based on ‘lenslet’ arrays rely on small and very-curved lenses which are not easy to manufacture and require specifically designed anti-reflection coatings to work efficiently. In addition, it is important to control of the systematic effects introduced by all the optical elements, from the telescope mirrors down to the detectors. These additional spurious signals need to be isolated and removed in order to avoid mixing them with the cosmological signals which we want to detect. Controlling the systematic effects requires deep understanding of the physics behind the functioning of each single component.
In this project we propose to develop high performance and compact lenslet arrays based on metamaterials. The Astronomy Instrumentation Group is world-leading in the design and production quasi-optical devices based on metamaterials, specifically using the ‘mesh-filters’ technology. We have recently developed flat ‘mesh-lenses’ able to accurately mimic the behaviour of thicker standard lenses. These lenses can be ’miniaturised’ and coupled to array of detectors. A mesh-lens array can be a simple flat device which includes all the small lenses.
The modelling and the design of these arrays will be carried out by using electromagnetic finite element analysis (Ansys HFSS). The devices will be manufactured and tested within the group cleanrooms and laboratories. The electromagnetic characterisation will be performed with Fourier Transform Spectrometers (FTSs) and Vector Network Analysers (VNAs).

The PhD research project will consist of:
• Metamaterials electromagnetic modelling using finite-element analysis software (HFSS)
• Design and optimisation of a novel lenslet array based on metamaterials
• Assistance in the manufacture of the device within the group facilities
• Device testing with Fourier Transform Spectrometers and Vector Network Analysers
• Analysis and interpretation of the data