Development of low critical temperature superconducting tunnel jucntions for application as photon detectors in astronomy

This thesis describes the development of low-energy gap superconducting tunnel junctions (STJs) for use as photon detectors, with as a main goal the improvement of the energy resolution in both the optical and the x-ray energy domain. A new model for the photon detection process with STJs is presented, which includes the full energy dependence of all the quasiparticle processes occurring in the junctions. This model allows for the calculation of the time- and energy-dependent quasiparticle distribution from the moment of generation of the quasiparticles by the photon absorption process until the end of the current pulse, when all the quasiparticles have disappeared.