Performance analysis of the heterodyne schlieren system

The performance of the electronic heterodyne schlieren system is investigated. The sensitivity, spatial resolution, and dynamic range of the system are calculated. It is shown that these features are improved compared with the conventional intensity schlieren readout technique. Without changing the system setup, the sensitivity and accuracy of the system can be tripled by using the third harmonic of the heterodyne signal. In this case, the spatial resolution and the measurement range are reduced by a factor of three. The system is self-calibrated. For whole field measurements, the method is limited by the camera to milliseconds time scale. However, for selected points measurements fast variations, the order of tens of microseconds, can be measured. The system was evaluated experimentally by measuring the focal length of a weak lens and a multiscale phase plate.