Detailed mapping of the interstrip response in double sided silicon strip detectors in front and back injection by means of IR laser irradiation

Silicon microstrips are widely used in nuclear physics experiments when high granularity and high resolution of the detection system is required, as, for example in particle-particle correlation measurements. In addition microstrip detectors are used in the field of X-ray detection for position resolved X-ray spectroscopy. In order to surgically probe the response of the interstrip region we tested the detector response matrix both in back and in front injection with an infrared pulsed laser at two different wavelengths (705 nm and 904 nm) in order to probe different ionization profiles. Depending on the side of interaction, on the position of incidence and on the absorption length, the shapes of the induced signals are significantly altered and signals of opposite polarity or bipolar signals arise. This phenomenon was already observed in the literature for other microstrip detectors but not analyzed in detail and no detailed laser mapping has been performed yet. In order to get a complete picture of the physical phenomena at the basis of the aforementioned behavior we performed detailed device simulations with a custom semi-analytical code and compared the experimental results with 3D simulations. The paper focuses on the description of the experimental measurements and their exhaustive interpretation.