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The Two Photon Absorption Transient Current Technique (TPA-TCT) is a tool to characterize semiconductor detectors using a spatially confined laser probe. Excess charge carriers are produced by the simultaneous absorption of two sub-bandgap photons in the material. The current induced by the motion of carriers is studied using well known TCT systems. Differently to standard TCT where the energy deposition (pair creation) is continuous along the beam, TPA-TCT reduces this region to an ellipsoidal volume, achieving thus, true 3D spatial resolution. This paper gives an overview of the technique and shows its performance in irradiated detectors, in particular diodes and High Voltage CMOS detectors., This work was performed in the framework of the CERN-RD50 collaboration under the projects 2016-04, 2017-02. Activity partially supported by the Spanish Ministry of Science grants FPA2015-71292-C2-2-P and FPA2017-85155-C4-1-R; and the European Union’s Horizon 2020 Research and Innovation program under Grant Agreement no. 654168 (AIDA-2020).

The requisites at the Large Hadron Collider (LHC) at CERN have driven silicon tracking detectors to the fringe of the modern technology. The next upgrade of the LHC to a 10 times increased luminosity of 7.5×10 cm s will require semiconductor detectors with substantially improved radiation hardness. CERN-RD50 collaboration mandate is to provide detector technologies, which are able to operate in such an environment. Within this context, this paper describes the approaches and first results of a C++11 multi-threading software based on the Shockley–Ramo's theorem to simulate non-irradiated and irradiated silicon micro-strips and pad detectors of complex geometries in order to understand signal formation and charge collection efficiencies of arbitrary charge distributions., This work was performed in the framework of the CERN-RD50 collaboration. This project has been partially supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under grant number FPA2013-48387-C6-1-P and FPA2015-71292-C2-1-P.

For the first time, the deep n-well (DNW) depletion space of a High Voltage CMOS sensor has been characterized using a Transient Current Technique based on the simultaneous absorption of two photons. This novel approach has allowed to resolve the DNW implant boundaries and therefore to accurately determine the real depleted volume and the effective doping concentration of the substrate. The unprecedented spatial resolution of this new method comes from the fact that measurable free carrier generation in two photon mode only occurs in a micrometric scale voxel around the focus of the beam. Real three-dimensional spatial resolution is achieved by scanning the beam focus within the sample., This work was performed in the framework of the CERN-RD50 collaboration under the project RD50-2015-03. The project has received funding from the European Commission under the FP7 Research Infrastructures project AIDA, grant agreement no. 262025. This project has been partially supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under grant number FPA2013-48387-C6-1-P.