Laser Ultrasonics on Moving Paper

Abstract The propagation velocities of laser-generated ultrasonic plate waves were measured on paper moving at 10 m s −1 using a Mach–Zender interferometer and scanning mirror. Fast- and slow-propagating plate wave vibrational modes were detected. Velocity measurements were made on four types of paper, perpendicular to and in the direction of paper motion. Laser-ultrasonic measurements of phase velocities for the fast-propagating vibrational mode were compared with contact transducer-based measurements. The effect on signal amplitude of (1) distance from the detection point to the ultrasound generation point and (2) the pulse energy of the ultrasound generation laser was studied using stationary paper.