Chromatic focus variation measurements realized using a metasurface for the focal shift

Focus variation microscopy is a non-contact technique for surface topography measurement, which utilizes the limited depth of focus of a microscope to allow the topography of a surface to be determined after it has been scanned through the focal plane. Recently, approaches using a chromatic dependence of the focal plane location, realized using multiple glass elements in a custom objective, have been developed that remove the need to physically scan elements. Here, we demonstrate how a metalens can be used to simultaneously deliver the focusing and wavelength-dependent focal shift required with only a single lightweight element, opening up the path to the development of ultra-compact lightweight focus variation instrumentation.