Search

Photothermal phenomenon is one of the natural responses in light-matter interactions in which the energy of the incident light is converted into heat, resulting in a temperature increase in the illuminated material. This effect has a direct influence on the refractive index of the material such that its change of spectral dependency with temperature can be exploited for different applications. However, it is also important to separate/identify the thermal effect from the optical/electronic resonance effect to expand potential applications of light-matter interactions. In this work, we demonstrate the use of a white-light interferometry approach combined with a windowed Fourier transform method and a consistency-checking peak-fitting method to obtain the refractive index of an Rh6G-ethanol dye solution with a sensitivity of about ∼10-6 (RIU) for the visible range. Moreover, we also perform both static and dynamic measurements to study the photothermal effect of the Rh6G solution under external excitation. Importantly, we separate the optical and thermal effects due to the external excitation and obtain very good agreement with the experimental results by modeling the relative refractive index of the Rh6G solution with an expression consisting of spectrally a Fano-like resonance term and a linear dependent thermal term. We find that the response due to the optical effect is about ∼0.2 × 10-3 of that due to the thermal effect in the low-light regime. Our approach to separating the optical and thermal effects could shed light on other fields for potential applications through precision measurements of the transmission phase or refractive index. © 2023 Optica Publishing Group.

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.

Based on the transfer-matrix method (TMM), we report the characteristics of the interface states in one-dimensional (1D) composite structures consisting of two photonic crystals (PCs) composed of binary dielectrics A and B, with unit-cell configurations ABA (PC I) and BAB (PC II). The dependence of the interface states on the number of unit cells N and the boundary factor x are displayed. It is verified that the interface states are independent of N when the PC has inversion symmetry (x = 0.5). Besides, the composite structures support the formation of interface states independent of the PC symmetry, except that the positions of the interface states will be varied within the photonic band gaps. Moreover, the robustness of the interface states against nonuniformities is investigated by adding Gaussian noise to the layer thickness. In the case of inversion symmetry (x = 0.5) the most robust interface states are achieved, while for the other cases (x ≠ 0.5) interface states decay linearly with position inside the band gap. This work could shed light on the development of robust photonic devices. © 2022 Current Optics and Photonics.

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. © 2021 Ranran Zhang et al., published by De Gruyter, Berlin/Boston 2021.

Circular phase-dichroism (CPD) has been suggested for the characterization of chiral metasurfaces in supplementing the conventional circular dichroism (CD). Conventional CD probes the bulk properties while the CPD, reported recently in 2D chiral metasurfaces using an air-gap Fabry-Perot setup, is based on the surface properties. Here we propose and demonstrate a robust birefringent interference approach to obtain the CPD by replacing the air-gap with a uniaxial birefringent material in which interference is realized by the difference in the refractive indexes for the ordinary and extraordinary components of the material. We measure the transmission phases of metasurfaces fabricated on birefringent sapphire substrates and obtain clear CPDs for chiral metasurfaces but vanishing for achiral metasurfaces. Importantly, our approach can be applied to metasurfaces fabricated on nonbirefringent substrates by add-on birefringent materials. We confirm our results by a Jones matrix method using data obtained from full-wave simulations, and good agreements with experiments are obtained.