In this letter, we experimentally report an achromatic metalens (AML)operating over a continuous bandwidth in the visible. This is accomplished viadispersion engineering of dielectric phase shifters: titanium dioxidenanopillars tiled on a dielectric spacer layer above a metallic mirror. The AMLworks in reflection mode with a focal length independent of wavelength fromwavelength of 490 nm to 550 nm. We also design a metalens with reversechromatic dispersion, where the focal length increases as the wavelengthincreases, contrary to conventional diffractive lenses. The ability to engineerthe chromatic dispersion of metalenses at will enables a wide variety ofapplications that were not previously possible. In particular, for the AMLdesign, we envision applications such as imaging under LED illumination,fluorescence, and photoluminescence spectroscopy.
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