Synchronized-scanning laser vibrometry

The use ofLaser Vibrometers incorporating some form ofmanipulation ofthe laser beam orientation, typically using two orthogonally aligned mirrors, has become increasingly popular in recent years with considerable attention being given to the operation of such scanning Laser Vibrometers in continuous scanning mode. Here the laser beam orientation is a continuous function oftime. making it possible, for example, to track a single point on a moving target such as a rotating bladed disc. A recently derived comprehensive velocity sensitivity model has been developed to incorporate timedependent beam orientation enabling confident and detailed analysis ofdata obtained in such measurements. The model predicts the measured velocity for arbitrary mirror scan angles and arbitrary target motion and is shown to be especially valuable in revealing the sources ofadditional components that occur in continuous scanning and tracking measurements on rotors. The development of the comprehensive velocity sensitivity model and of sophisticated measurement hardware and software has resulted in proposal of the exciting new Synchronised-Scanning Laser Vibrometry technique. Introduced for the first time in this paper, the measurement involves the probe laser beam tracking the rotating structure and simultaneously scanning the region of interest to provide modal data under operating conditions, i.e. during rotation. Such a measurement is inconceivable by any other means and the system that has been created has the potential to provide data offundamental importance in the design and development ofa wide range ofdevices from hard disk drives to gas turbines.