Active phase-control metasurfaces show outstanding capability in the active manipulation of light propagation, while the previous active phase control methods have many constraints in the cost of simulation or the phase modulation range. In this paper, we design and demonstrate a phase controlled metastructure based on two circular split ring resonators (CSRRs) composed of silicon and Au with different widths, which can continuously achieve an arbitrary Pancharatnam-Berry (PB) phase between -π and π before or after active control. The PB phase of such a metasurface before active control is determined by the rotation angle of the Au-composed CSRR, while the PB phase after active control is determined by the rotation angle of the silicon-composed CSRR. And active control of the PB phase is realized by varying conductivity of silicon under an external optical pump. Based on this metastructure, active control of light deflection, metalens with arbitrary reconfigurable focal points and achromatic metalens under selective frequencies are designed and simulated. Moreover, the experimental results demonstrate that focal spots of metalens can be actively controlled by the optical pump, in accord with the simulated ones. Our metastructure implements a plethora of metasurfaces’ active phase modulation and provides applications in active light manipulation.

The carrier dynamics and time-dependent photo-physical properties in the degradation period of hybrid organic-inorganic lead halide perovskites (HOIPs) are still unclear. Here a non-contact optical pump THz probe measurement was performed to observe the long-term degradation process of 2D passivated and cesium stabilized formamidinium lead iodide perovskite (FAPbI₃) films. We find that photoconductivity and carrier mobility of the FA_0.9Cs_0.1PbI₃ film decay steadily, while these of the 2D phenylethylammonium lead iodide (PEA₂PbI₄) passivated FAPbI₃ film show an accelerated decay rate. Moreover, it’s also revealed that the localization of charge carriers increases with the transformation process from the fitted results by the Drude-Smith model. These results indicate that the stabilized effect of Cs incorporation is continuous, while the passivated effect of PEA₂PbI₄ can be weakened by the newly emerged phase boundaries. This report proposes a new perspective and sheds light on the degradation process of HOIPs.

A compact 110 GHz scattering-scanning near-field microscope is proposed and demonstrated. With employing a sub-harmonic IQ mixer as the dual-output demodulator, the microscope successfully acquires steady and background-free near-field-phase and -amplitude images with a resolution of ~130 nm, and obtains the ability of the all-time capture of near-field phase information under ambient conditions. To optimize the performance of microscope, the signal-extraction algorithm and influences of tip parameters on image quality are also introduced and analyzed in detail. It has been proven that the experimental results are quite consistent with our theoretical analysis. Besides, refer to present instrument setup and signal-extraction algorithm, the microscope has the potential to be expanded to higher operating frequency bands. These indicate that the microscope is a promising tool to realize the high-quality nano-imaging in low-terahertz band.