• perturbation crystallography;
  • X-ray detectors;
  • large dynamic range;
  • germanium photodiodes.

An IR detector based on a cooled germanium photodetector has been tested for applications in X-ray diffraction. The detector can be used simultaneously in photon-counting mode and current mode giving a dynamic range from < 1 to 109 photons s−1. Since germanium is used as the photodetector, its efficiency at energies above 25 keV is much better than the silicon equivalents. The detector proved to be highly linear both in the low-flux region (< 105 photons s−1) where photon counting is used and in the high-flux region (> 105 photons s−1) where the detector is run in current mode. The response time of the detector is of the order of 1 μs, making it suitable for studies in perturbation crystallography, especially when coupled to a lock-in amplifier. As an example, the shift of a reflection of LiNbO3 induced by an external electric field was determined with the germanium detector and lock-in amplifier.