A spatially resolving detector for heat-pulse experiments

A new technique for spatially resolved detection of heat pulses (phonons) at liquid-helium temperatures is described. Unlike existing phonon imaging methods, this system is not affected by the presence of magnetic fields up to at least 7 T. The method utilises a spatially extended cadmium sulphide thin film as a phonon bolometer. Small (<200 mu m) regions of the film are selectively sensitised by a microcomputer-controlled, scanned laser spot and 'reset' after data acquisition using a large ( approximately=50 mA) current pulse. Using data acquisition and analysis software, line scans of the transmitted phonon intensity as a function of propagation direction are obtained. Sample data of the phonon intensity in the (110) plane of silicon are presented.