Gain suppression in LGAD detectors under focused and defocused femtosecond laser beam

Abstract

Low Gain Avalanche Diodes (LGADs) are particle detectors with a moderate gain ($<$ 50) optimized for high energy physics experiments. Gain in these sensors is controlled by bias voltage but it depends also on the other factors such as temperature and charge density generated in the gain layer. When the laser pulses are used to study LGADs, charge density strongly depends on the beam parameters. The same laser intensity can induce different charge density across the gain layer if the focusing parameters vary. It is known that higher ionization densities cause reduction of the gain and this effect has been already investigated. Here, we present extension of the previous gain suppression studies investigating not only spatial, but also temporal distribution of the laser pulses. In addition, we demonstrate gain suppression effect at two different wavelengths commonly used in characterization of the silicon detectors.