Role of Active Chiral Plasmonic Phase-Change Metasurface in Tunable Photothermal Conversion and Optofluidics.

Here, we report the design of a plasmonic active chiral metasurface with the ability of tuning spectral absorption circular dichroism (CDA). A few studies have addressed the optical chirality on heat generation in a chiral metasurface and thermal-induced fluid convection. Furthermore, the framework of designing an active device on photothermally induced fluid motion is still unexplored. This paper demonstrates an optical active chiral phase change material-based metasurface by leveraging the reversible monoclinic-rutile phase transition in VO2. The structure exhibits two giant wavelength-dependent CDA in the VO2 monoclinic state, which undergoes blue-shift upon VO2 phase transition into the rutile phase. It leads to the strong and tunable photothermal circular dichroism. It facilities the concept of tunable optofluidic circular dichroism through mulitiphysics analysis of optics, thermodynamics, and hydrodynamics. The results show how the active chiral nanaostructure can induce the tunable fluid convection velocity not only under circularly polarized (CP) excitation but also on distinct tunable resonance wavelengths with VO2 phase transition. Moreover, the wavelength-dependent photothermal heat profile and photothermally induced fluid velocity closely follows the absorption spectra trend under CP illumination and at both states of VO2 indicating the wavelength-selective photothermal and optofluidic response of the nanostructure. The concept of this work establishes a platform for polarization-sensitive chiral absorber and tunable photothermal systems, chiral biology and reconfigurable optofluidic systems, and so on.