Laser ultrasonics for noncontact measurement of lamb waves in static and moving paper

The experimental demonstration of noncontact laser ultrasonics to monitor L amb waves and the relevant mechanical behaviour of paper is presented. Meas urements were performed in a controlled environment using a variable-speed web simulator. Signals obtained using the photorefractive method on nonmovi ng paper are discussed and the preliminary analysis of S-0 and A(0) modes i s presented On moving paper the detection of ultrasonic signals based on th e Photo-EMF interferometer technology is reported at production speeds on c opy paper and 42 Eb linerboard. Preliminary results verify the potential of laser ultrasonics for real-time monitoring of elastic stiffness, bending s tiffness and shear rigidity.