Liquid‐Crystal‐Enabled Varifocal Achromatic Metalens

Abstract Integrated planar optical devices with dynamic functionalities are in high demand in the rapidly developing terahertz region. In particular, varifocal achromatic metalenses are urgently needed for biochemical discrimination imaging and nondestructive inspection. Here, a design is proposed to realize a varifocal achromatic metalens. It works on the simultaneous compensation of the diffraction dispersion of a foci‐switchable basic phase profile on the basis of a properly preset group delay of a propagation phase. The concept is demonstrated with a liquid crystal integrated silicon metalens. The major axis orientation of cylindroid meta‐atoms supplies a fixed geometric phase, the photopatterned liquid crystal provides a switchable geometric phase, and the compensation originates from the shape variation of cylindroid meta‐atoms. Both simulations and experiments verify the switchable achromatic focusing at two distinct foci (10.20 and 13.76 mm) across 1.0–1.6 THz. Dual‐depth multispectral imaging is further demonstrated with two medicaments, exhibiting its potential for nondestructive safety screening and pharmaceutical identification. The proposed strategy establishes a framework for next‐generation adaptive terahertz techniques and applications.