Experimental confirmation of phase profile of Hermite–Gauss beams

Phase distribution of Hermite-Gauss (HG) beams generated by a gas laser is investigated experimentally by studying their interference with a plane wave and diffraction by a single slit by selecting pairs of bright lobes with different phases. Experimentally recorded interference and diffraction profiles support HG mode phase profiles expounded on in this paper. We find that the phase difference between one bright lobe and another is not simply zero or <i>π</i> but increases (or decreases) uniformly in steps of <i>π</i> as the number of zeros between them increases, in agreement with analytic function theory. An immediate application of this phase profile is that an HG mode can serve as a phase ruler with bright lobes as markers in steps of <i>π</i>.