Millimetre and submillimetre bolometric interferometry

• Main Author: Campbell, E. S.
• Published: University of Cambridge 2005
• Subjects: 530.0724
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597259

I start by presenting simulations of the noise performance of Superconductor-Insulator-Superconductor (SIS) direct detectors, combined with op-amp based readout electronics. This involves the combination of non-linear device modelling, with a detailed noise model of both the SIS junction and the readout-electronics. Using this model, I show that an SIS direct detector can be competitive in terms of noise performance with a transition edge sensor, provided the junction is biased well below the gap, and that the gap is tailored to the observing frequency. I then describe a set of experiments aimed at measuring the noise performance of a tantalum aluminium SIS device combined with op-amp based readout. I compare the results of these experiments with the predictions of my model, and show that they are in excellent agreement. Using the modelling software I have developed, I predict the lowest noise equivalent power achievable with this device as being 1.3 x 10^-17W/√Hz, over a video bandwidth of 5 kHz. The expected dynamic range is 91 dB. I also describe the development and testing of the first submillimetre, single-chip, beam combining interferometer. This uses a superconducting chip, on which both the beam combination and detection occur. Two designs of chip were tested, one using a directional coupler for the beam combination, the other using a 90° hybrid. Both designs resulted in the measurement of fringe patterns that agree remarkably well with theory. The final part of this work concerns the development of a new modal theory of interferometry. The aim of this work was to accurately describe the partially coherent behaviour of multi-moded bolometric interferometers. My first attempt uses an approach based on the eigenmodes of the optical system. This was successful, but it became apparent that a more elegant solution existed. This alternative approach introduces the concept of eigenfields. These are the fundamental field distributions associated with an optical system. The can be found using the singular value decomposition, and, as I demonstrate, they allow the accurate simulation of multi-modal bolometric interferometers.