Metasurfaces with ultrathin artificial structures have attracted much attention because of their unprecedented capability in light manipulations. The recent development of metasurfaces with controllable responses opens up new opportunities in various applications. Moreover, metasurfaces composed of twisted chiral structures can generate asymmetric responses for opposite incidence, leading to more degrees of freedom in wave detections and controls. However, most past studies had focused on the amplitude responses, not to mention using bi‐directional phase responses, in the characterization and light manipulation of chiral metasurfaces. Here, we report a birefringent interference approach to achieve a controllable asymmetric bi‐directional transmission phase from planar chiral metasurface by tuning the orientation of the metasurface with respect to the optical axis of an add‐on birefringent substrate. To demonstrate our approach, we fabricate planar Au sawtooth nanoarray metasurface and measure the asymmetric transmission phase of the metasurface placed on a birefringent sapphire crystal slab. The Au sawtooth metasurface‐sapphire system exhibits large oscillatory behavior for the asymmetric transmission phase with the tuning parameter. We confirm our experimental results by Jones matrix calculations using data obtained from full‐wave simulations for the metasurface. Our approach in the characterization and light manipulation of metasurfaces with controllable responses is simple and nondestructive, enabling new functionalities and potential applications in optical communication, imaging, and remote sensing.

The ability of chiral media to differentiate circularly polarized light is conventionally characterized by circular dichroism (CD) which is based on the difference in the absorption of the incident light for different polarizations. Thus, CD probes the bulk properties of chiral media. Here, we introduce a new approach termed as circular phase‐dichroism that is based on the surface properties and is defined as the difference of the reflection phase for different circularly polarized incident lights in characterizing chiral media. As a demonstration, we measure the reflection phase from planar chiral sawtooth metasurface for circularly polarized light in the visible range using a simple Fabry Perot interference technique. The measured circular phase‐dichroism is also crosschecked by conventional CD measurement of the transmitted light and by full‐wave simulations. Our results demonstrate the potential applications of circular phase‐dichroism in sensing and metasurface characterizations.

We report the fabrication of a solidly mounted resonator (SMR) that can also function as a sensor for biological molecules. The SMR, consisting of a Au electrode, aluminum nitride (AlN) piezoelectric thin film and Bragg acoustic reflector, was fabricated on a Si substrate by radio frequency (RF) magnetron sputtering. The Bragg acoustic reflector, made entirely of metal, has small internal stress and good heat conduction. Human immunoglobulin G (IgG) antibody was immobilized on the modified (by self-assembled monolayer method) Au electrode surface of the SMR and goat anti-human IgG antigen was captured through the specificity of bond between the antibody and antigen on the electrode surface. We found a linear relationship between the resonant frequency shift and the concentration of goat anti-human IgG antigen for concentrations smaller than 0.4 mg ml⁻¹ and a relatively constant frequency shift for concentrations greater than 0.5 mg ml⁻¹. A series of interference experiments can prove that the selectivity of the sensor is satisfactory. Our findings suggest that the SMR sensor is an attractive alternative for biomolecule detection.

Laser propulsion of a graphene sponge shows tremendous potential in propellant-free flight, photoresponsive actuators and micro opto-electro mechanical systems. However, the mechanism is still in dispute and the propulsion force hasn’t been accurately measured, seriously hindering its development. This work develops a quantitative method to measure the propulsion force. It is found that the characteristics of the force agree qualitatively with the Knudsen force due to laser-induced thermal nonequilibrium in rarefied gas, which might be another possible mechanism of laser propulsion of a graphene sponge. Also, this kind of laser propulsion is highly efficient, stable and sustainable.

Optical pulling is an attractive concept due to the counterintuitive feature, the profound mechanism underneath and promising applications. In recent ten years, optical pulling of micro-nano objects have been fully demonstrated. However, optical pulling of a macroscopic object is challenging. Herein, laser pulling of a macroscopic object is presented in rarefied gas. The pulling force is originated from the Kundsen force when a gauss laser beam irradiates a macroscopic structure composed of the absorptive bulk cross-linked graphene material and a SiO₂ layer. A torsional pendulum device qualitatively presents the laser pulling phenomenon. A gravity pendulum device was used to further measure the pulling force that is more than three orders of magnitudes larger than the radiation pressure. This work expands the scope of optical pulling from microscale to macroscale and provides an effective technique approach for macroscopic optical manipulations.

A passively Q-switched compact dual-wavelength Er: SrF₂ laser, operating at a 2729.73 nm and 2747.2 nm wavelength, was demonstrated by utilizing CsPbCl₃ quantum dots (QDs) as a saturable absorber (SA). The maximum average output power with the shortest duration of 510 ns and a repetition rate of 45 kHz was achieved at 190 mW, and the corresponding maximum single pulse energy and the peak power were 73.69 μJ and 141.7 W, respectively. The results present an efficient dual-wavelength laser source, and the halogen perovskite quantum dot has the potential to be employed as an excellent saturable absorber in mid-infrared pulsed solid-state lasers.