Fast, multi-band photon detectors based on quantum well devices for beam-monitoring in new generation light sources

In order to monitor the photon-beam position for both diagnostics and calibration purposes, we have investigated the possibility to use InGaAs/InAlAs Quantum Well (QW) devices as position-sensitive photon detectors for Free-Electron Laser (FEL) or Synchrotron Radiation (SR). Owing to their direct, low-energy band gap and high electron mobility, such QW devices may be used also at Room Temperature (RT) as fast multi-band sensors for photons ranging from visible light to hard X-rays. Moreover, internal charge-amplification mechanism can be applied for very low signal levels, while the high carrier mobility allows the design of very fast photon detectors with sub-nanosecond response times. Segmented QW sensors have been preliminary tested with 100-fs-wide 400 nm laser pulses and X-ray SR. The reported results indicate that these devices respond with 100 ps rise-times to such ultra-fast laser pulses. Besides, linear scan on the back-pixelated device has shown that these detectors are sensitive to the position of each ultrashort beam bunch.