WIDE DYNAMIC-RANGE GERMANIUM DETECTOR FOR PERTURBATION CRYSTALLOGRAPHY

An IR detector based on a cooled germanium photodetector has been test ed for applications in X-ray diffraction. The detector can be used sim ultaneously in photon-counting mode and current mode giving a dynamic range from <1 to 10(9) photons s(-1). Since germanium is used as the p hotodetector, its efficiency at energies above 25 keV is much better t han the silicon equivalents. The detector proved to be highly linear b oth in the low-flux region (<10(5) photons s(-1)) where photon countin g is used and in the high-flux region (>10(5) photons s(-1)) where the detector is run in current mode. The response time of the detector is of the order of 1 mu s, making it suitable for studies in perturbatio n 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.