Thesis defense of Sebastian Pape

Modern high energy physics experiments have increasing demands on particle detectors in terms of their spatial and temporal resolution, as well as their ability to withstand higher radiation levels. To meet these demands, increasingly complex detectors with ever smaller device segmentations are being developed that require precise device characterisation. This work is dedicated to a newly developed characterisation technique: the two photon absorption - transient current technique (TPA-TCT); a method to characterise particle detectors with micrometer-scale three-dimensional spatial resolution. Femtosecond laser light with a wavelength in the quadratic absorption regime is focused to generate excess charge by two photon absorption in a volume of about 75 µm3 around the focal point. The drift of the excess charge carriers is studied to obtain information about the device under test. In this work, silicon detectors are used to explore and further develop the TPA-TCT. The technique is applied to pad detectors in order to study the technique and to strip and monolithic detectors to demonstrate the potential of TPA-TCT for the characterisation of state-of-the-art detector technologies. The applicability of the TPA-TCT in neutron, proton, and gamma irradiated devices is shown and radiation damage related effects on the technique are systematically studied. The reduction of charge multiplication in a low gain avalanche detector for increasing excess charge densities is observed and the role of diffusion to partially recover the gain is investigated. New techniques to investigate the electric field in complex segmented devices are developed and applied to strip and monolithic detectors. This work paves the way for the TPA-TCT as a tool to characterise detectors with three-dimensional micrometer-scale spatial resolution.

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