A FAR-INFRARED HETERODYNE SIDE-BAND SPECTROMETER

We present recent experimental developments in far-infrared coherent s pectroscopy. Most known far-infrared sidebands spectrometers use the d irect detection scheme. The system developed at Lille operates in the heterodyne mode. This technique offers particular advantages when larg e detection instantaneous bandwidths are needed, as could be the case in time resolved spectroscopy. As a counterpart of a heavier electroni c receiver system, the filtering constraints in the optical path are t otally eliminated, leading to a potential lowering of the overall nois e system. The receiver operates very close to physical limits. A caref ully designed optical line, incorporating only reflective components, allows to keep optical losses at very low levels, on the whole operati ng range. By using particular laser injection coupling and power extra ction schemes, reasonable short and long term stability has been achie ved in sidebands power generation. Some spectroscopic results illustra ting sensitivity and resolution capabilities are presented.