Ultrasonic attenuation is a combination of material losses and geometric effects. The current research quantifies the geometric effects in the far‐field, where the individual modes of a Lamb wave become separated. The overall ultrasonic signal, which is a superposition of these modes, depends on geometry, source type and individual mode characteristics. This research considers the amplitude decay of Lamb waves in an isotropic plate that are generated with an ablation source. A numerical simulation is developed using normal mode expansions, and is used to calculate amplitude decay. These numerical results are verified with an experimental program that uses laser generation and detection of multi‐mode, Lamb waves. © 2004 American Institute of Physics