Isotropic Ge3Sb2Te6 metasurfaces for mid-infrared wavefront steering

-Due to unprecedented electromagnetic properties, germanium antimony telluride (GST) plays a crucial role in the field of electromagnetic wavefront control. With the purpose of mid-infrared wavefront reconfiguration, eight Ge3Sb2Te6-based meta-atoms are proposed. Meta -atoms appear in different phase states as Ge3Sb2Te6 state is switched. As crystalline Ge3Sb2Te6 is involved, eight meta-atoms reach full phase coverage with phase gradient of 45 degrees. As Ge3Sb2Te6 is switched to amorphous state, phase difference between adjacent meta-atoms no longer varies uni-formly by 45 degrees, thus losing original properties. Based on eight meta-atoms, four metasurfaces are presented to verify characteristics, which are two metalenses and two orbital angular momentum (OAM) generators. As crystalline Ge3Sb2Te6 is switched to amorphous Ge3Sb2Te6, dynamical manipulation between focusing and defocusing is realized. Besides, OAM mode of vortex beam is reconstructed from l = 1 or 2 to l = 0. Our designs could find potential applications in focusing, switching, and encryption.Copyright & COPY; 2023 EPLA