Holographic metrology for study and evaluation of vibration in complex structures

Holographic interferometry has been applied to in situ measurements of vibration fields of large diameter conduits undergoing unsteady internal excitations. The ambient conditions under which the measurements were carried out were extremely difficult. The measurements, covering an area of several square meters with each holographic recording, were performed using a portable one joule pulsed ruby laser system capable of producing two sequential Q-switched pulses each with duration of similar to 25 ns with a variable pulse separation between 10 and 800 mu s. The entire assembly of laser and holographic camera was constructed as a single unit incorporating an internal reference beam; the reference beam included a mirror with the facility to make an angular tilt between the two laser pulses with the objective of providing a facility to obtain information relating to the phase of antinodes within the recorded area of the hologram.