Laser rotational vibrometers and their application in modal analysis

Many vibration engineers are now familiar with single beam Laser Vibrometers which are suitable for translational vibration measurements but fewer are familiar with Laser Vibrometers with a pair of parallel probe beams which are used for rotational vibration measurements. This paper explains why the parallel beam configuration is so effective, comparing this with early uses of cross-beam arrangements and concluding with an application of these so-called ‘Rotational Vibrometers’ in the evaluation of a torsional absorber using modal analysis.