National Research Council of Canada

Denis Drolet

Jean-Pierre Monchalin

Alain Blouin

Christian Padioleau

Philippe Delaye

Gerald Roosen

In order to probe an object in motion subject to surface displacement, for example, caused by ultrasonic wave propagation, a laser beam is split into a first portion and a second portion. The first is scatted off the object to generate a signal beam. The frequency shift produced in the signal beam due to motion of the object is measured, and this is used to adjust the frequency of one or both portions of the laser beam so that both beams have substantially the same frequency. The surface displacements are measured by comparing the second portion of the laser beam and the signal beam after frequency adjustment.

Ultrasonic vibration detection using frequency matching

A method and apparatus are provided of optically detecting transient motion from the surface of a workpiece. After directing a laser beam onto a surface of a workpiece the beam is reflected from it and then interferes with a pump beam removed from the laser source, inside a real-time holographic material, so as to form a grating diffracting the pump beam into a reference beam, which interferes at the output of the real-time holographic material with the received light beam, so as to produce a signal representative of the surface transient motion. An electric field is applied to the holographic material of sufficient magnitude to increase substantially the intensity of said reference beam and to give to this beam a phase differing substantially from the phase of said received light beam. The electric field is applied prior to the transient motion to be detected, for a time interval sufficiently long so as to capture the transient motion but sufficiently short a duration so as to avoid excessive heating of the real-time holographic material. The pump beam is of sufficiently high intensity so as to cause the response time of the real-time holographic material to be substantially shorter than a characteristic time defined as the time during which the phase of the received light, on average across its spatial distribution or locally, is not substantially changed.

Growing community of inventors

Montreal, Canada

Denis Drolet