Laser ultrasonics on moving paper

The propagation velocities of laser-generated ultrasonic plate waves were m easured on paper moving at 10 m s(-1) using a Mach-Zender interferometer an d scanning mirror. Fast- and slow-propagating plate wave vibrational modes were detected. Velocity measurements were made on four types of paper, perp endicular to and in the direction of paper motion. Laser-ultrasonic measure ments of phase velocities for the fast-propagating vibrational mode were co mpared with contact transducer-based measurements. The effect on signal amp litude of (1) distance from the detection point to the ultrasound generatio n point and (2) the pulse energy of the ultrasound generation laser was stu died using stationary paper. (C) 1999 Elsevier Science B.V. All rights rese rved.