Design and performance of a high-resolution dual-channel heterodyne laser velocimeter

We describe a dual-channel laser velocimeter based on a single laser source and a single set of carrier wave generation optics. The apparatus is intended for simultaneous vibration measurements on several points of instable objects, such as biological specimens or micro electronic mechanical systems, so that instantaneous phase relationships and amplitude ratios can be determined. Our instrument presently allows measurements on two points of interest which can be arbitrarily chosen. The optical design allows expansion to at least four independent channels. At a maximal velocity amplitude of 52 mm s−1, the velocity resolution and the detection limit equal 2.6 μm s−1 Hz−1/2. Even with object points less than 0.4 mm apart, channel cross-talk is less than −78 dB at all frequencies.