Laser Excitation of a Fracture Source for Elastic Waves

Thomas E. Blum, Boise State University
Kasper van Wijk, Boise State University
Roel Snieder, Colorado School of Mines
Mark E. Willis, ConocoPhillips

Abstract

We show that elastic waves can be excited at a fracture inside a transparent sample by focusing laser light directly onto this fracture. The associated displacement field, measured by a laser interferometer, has pronounced waves that are diffracted at the fracture tips. We confirm that these are tip diffractions from direct excitation of the fracture by comparing them with tip diffractions from scattered elastic waves excited on the exterior of the sample. Being able to investigate fractures—in this case in an optically transparent material—via direct excitation opens the door to more detailed studies of fracture properties in general.