Investigation of capillary waves excited by a Nd:YAG laser using pyrometry

A mechanism for excitation of capillary waves on a weldpool formed by a laser is shown to be due to coupling of the weldpool height with the laser beam profile. This leads to an additional low frequency mode, which has been observed and has a frequency of about an order of magnitude lower than the classically expected capillary waves. This mechanism for wave excitation on the weldpool can only happen if the focal point of the laser beam is located above the surface of the weldpool; otherwise the waves are damped.