Development of transition edge sensor distributed read-out imaging devices for applications in x-ray astronomy

This thesis is concerned with the development of, position-sensitive, Transition Edge Sensors (TES) operating at cryogenic temperatures (~ 0.1 K). The Distributed Read-Out Imaging Device (DROID) concept uses TES read-out at both ends of a linear X-ray absorber, to derive, through heat diffusion, both spectral and spatial information. Potentially, DROIDs offer a simpler technological alternative to the development of large area pixel arrays for future X-ray space observatories (Chapter 1). Chapter 2 presents a comprehensive review of the theory of microcalorimeter detectors. A finite-element model is established in Chapter 3, to numerically simulate the response of the DROID to an X-ray photon, as well as the noise spectral density at the detector outputs, including frequency dependent correlations between the two TESs. In Chapter 4 this model is used to implement pre-existing algorithms, based on the use of the optimal filter, to calculate the position and energy resolution along the length of experimental DROID designs. We show that these algorithms do not lead to optimum performance under all conditions and then derive the true optimal filters, based on least-squares minimisation of the total noise power in the DROID. By numerical simulation we show that significant improvements in both the energy and in particular, the position resolution, are theoretically possible. The design and experimental characterisation of two prototype DROIDs are described in Chapter 6 and 7, using the equipment described in Chapter 5. The first X-ray results from a prototype TES DROID, using single TES read-out, are reported. These results demonstrate proof of concept, confirming spatial sensitivity along the DROID, through the actual spectral and spatial resolutions are limited by the availability of only a single read-out channel.