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

Focus variation microscopy is a non-contact technique for surface topography measurement which utilises 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, realised 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 focussing and wavelength dependant focal shift required with only a single lightweight element, opening up the path to the development of ultra-compact lightweight focus variation instrumentation.