Direct measurement of the dispersion relation of capillary waves by laser interferometry

Surface waves on fluids with wavelengths in the millimeter range are known as capillary waves. Surface tension determines the propagation and dispersion of capillary waves while gravity plays a minor role. We describe a simple method for generating standing capillary waves of known frequency on water and introduce a novel noncontact technique based on laser interferometry to measure the wavelength of capillary waves with great precision. The data gives the dispersion relation of capillary waves and provides an accurate method for determining the surface tension of fluids. (c) 2006 American Association of Physics Teachers.