Novel design of MCT-detector optics with enhanced performance

Abstract

In high resolution Fourier transform spectroscopy photoconductive MCT-detectors are widely used for measurements in the mid infrared region. In order to minimize measurement time and maximize precision a high signal to noise ratio (SNR) achieved for source photon noise and minimized background photon noise conditions is essential. A novel detector optics design for the Bruker IFS 120/125 is presented, consisting of a commercial 1 mm area AG&G MCT detector chip (cutoff 725 cm-1 @ 77 K, 640 cm-1 @ 45 K), selectable cooled aperture, cooled optical filter and two imaging and one flat mirror which are placed in a standard Infrared Labs cryostat. The cryostat is cooled to 45 K instead of the usual 77 K to suppress thermal excitation noise. The performance of the detector unit was tested with a Bruker IFS 125 HR versus an Infrared Associates D316 detector unit as supplied usually by Bruker. As expected the new unit shows significantly higher SNR especially when operated with narrowband optical filters. It is also shown that optical modifications inside the Bruker have minor influence on the performance.