Whole field vibration measurements with laser-based techniques

Abstract

This paper discusses two techniques, a time-domain technique and a space-domain technique, to remotely measure 2-D vibration characteristics of a surface. The first technique is based on using multiple diode laser vibrometers to simultaneously measure the surface vibration at multiple points. The principles of laser Doppler vibrometry are briefly discussed and various architectures of systems to perform landmine detection are presented and discussed. Surface velocity data corresponding to various types of soils shaken by a buried geophone are presented. The second technique is based on laser speckle interferometry using a single digital camera to instantaneously capture quantitative phase information. The phase information of two consecutive frames is then converted to velocity profiles of the vibrating surface. The principles of a new method to perform instantaneous phase shifting interferometry are presented and modal analysis data of turbine blades obtained with an all-digital optical system are discussed.