US Patent 7516662 Detecting rail defects

A method of detecting defects in a railway track rail, the rail (101) having a longitudinal centre plane and a surface, the surface including a running surface (102), the method comprising directing an excitation laser beam (106) to an excitation position (103) on the surface of the rail (101) to induce an ultrasonic wave in the rail (101); and directing a detection laser beam (108) to a detection position (104) on the surface of the rail (101) to detect at least one predetermined property of the induced ultrasonic wave; wherein the excitation position (103) and the detection position (104) are located on the running surface (102) and displaced from the longitudinal centre plane of the rail (101).