A Scanning Laser Line Source (SLLS) technique is demonstrated using a true thermoelastic line source which leads to generation of monopolar Rayleigh waves. As the SLLS is scanned over a surface‐breaking flaw, the monopolar signal is shown to become bi‐polar, dramatically indicating the presence of the flaw. The SLLS technique is demonstrated both experimentally and numerically through hybrid mass‐spring lattice simulations. Experiments for the SLLS technique are performed using a line focused Nd:YAG laser and an interferometric detector. Both numerically‐ and experimentally‐generated Rayleigh waves show characteristic monopolar shape in the absence of flaws and become bi‐polar as the SLLS approaches the flaw. Numerical simulations performed to gauge the effect of crack depth on the SLLS signatures demonstrate that the technique can also be used to size cracks. © 2004 American Institute of Physics