A Measurement of the Gouy Phase after a Slit

The Gouy phase is a characteristic phase change with respect to a plane wave at an optical caustic, which can be explained as the consequence of momentum conservation at a light path confinement. Since this phase can be calculated with the Huygens-Fresnel diffraction theory and appears also in the path integrals of massive quantum particles, its measurement is of high interest for an understanding of the basic structure of physics. In order to verify our calculations of the Gouy phase (Frins et al. DGaO Proc. 2015), we measured it after a slit of varying width with the help of a Mach-Zehnder interferometer. The measurement confirms our previous result, namely that the 1/i –factor in the Huygens-Fresnel diffraction theory compensates the Gouy phase at the test point after the aperture and that it is described by the Fresnel integrals.