Measuring multiscale capillary curvature using laser beam self-interference

When a parallel light beam illuminates a curved air–liquid interface, a group of self-interference fringes appears in the reflection field in the region near the critical point. A model describing the interface height and slope dependences on the fringe phase supports this observation. The fringe phase function is determined by the fringe image. The height, slope, and curvature of the interface curved by a glass slide and thin rod are measured. The resolution, for the curvature measuring, is up to 0.05μm−1. A comparison of the experimental results of the interface height by using the exponential theory verifies this approach’s reliability. A small RMS error shows that the results are in good agreement. •Self-interference fringes appears in the reflection field firstly when a parallel light beam illuminates an air–liquid curved interface.•A technique for air–liquid interface visualisation, based on self-interference from air–liquid curved interface, is developed with real-time feature.•The research may provide an alternative detection technology for air–liquid interface in a multitude of industrial and medical applications.