Resistive memory devices are new type of non-volatile memory devices that can be switched between high resistance state (HRS) and low resistance state (LRS) under the action of an external electric field. The selection and interaction of electrode materials and active layer materials are the main factors for realizing the resistive switching characteristics of devices. Graphene is a two-dimensional (2D) material with excellent electrical conductivity and high ductility. Reduction of graphene oxide (GO) by laser processing is an excellent method to obtain graphene efficiently. The preparation process of traditional memory devices is complicated, which is not conducive to large-scale processing and manufacturing. Using metal Au and reduced graphene oxide (rGO) as electrodes, and GO as the active layer for device fabrication, the resistive switching function of the memory device is well realized. The simple and efficient fabrication method provides a reference for the large-scale and highly integrated production of resistive memory devices.

The current surgical navigation system requires the doctor’s sight to switch back and forth between the display screen and the patient, which can easily cause visual fatigue and affect the safety of the operation. In response, an optical surgical navigator based on mixed reality was introduced herein, which enabled the navigation information to be directly fused into the surgical area. The navigator was based on mixed reality (MR) glasses and a binocular vision tracker system. A novel virtual-real registration scheme was proposed, which established the mapping relationship between the virtual model coordinate system and the real world based on the tracker measurement. The wireless communication between the data processing unit and the MR glasses was realized, and the virtual model can be overlapped with the patient’s surgical area for real-time navigation. The accuracy of the optical navigator was verified with the virtual-real fusion display experiment based on a skull model sample. The results show that the dislocation error between the virtual model and the real sample is about 4.5 mm, and the display refreshing rate reaches about 15 frames per second, which can verify the feasibility of the proposed scheme and its potential for practical clinical application.

In this letter, a pure geometric phase based all-dielectric metalens is designed and aimed to enhance the tolerance of imaging in the longitudinal direction. Numerical simulation for the designed metasurface is carried out using the pure geometric phase spin decoupling design method combined with the finite difference time domain (FDTD) method. The calculated results show that designed metasurface enables the characteristics of controllable polarization and extended focal length, achieving a focal depth of 8 mm along the propagation direction, compared with 4.5 mm for a conventional metalens. Furthermore, we also design and numerically validate a terahertz metalens that can generate two focal points with extended focal length, and the polarization states of the two extended focal points are orthogonal to each other, demonstrating the multiplexing functionality of the designed metalens. The unique and effective approach may open a new avenue for tomography and information encryption.

The focus of this paper is the sub-wavelength imaging of gradient index photonic crymstals. The gradient index photonic crystals is a parallel plate composed of silicon and circular air holes. The gradient change of photon crystal refractive index is realized by adjusting the structure of each column of pores. The focusing process of the gradient index photonic crystals is simulated by finite-different time-domain (FDTD) algorithm. The results showed that proper modification of the optical path difference could greatly optimize the focusing effect. Furthermore, changing the focal length of photonic crystals and the structure of the central air hole could also optimize the focusing effect. By combining the above three elements, the gradient index photonic crystal was finally designed which could realize sub-wavelength focusing. The half-width of the focused spot was 0.3447 λ , which was located at 1.45 λ outside the photonic crystal. To improve application performance, a dynamic focal length adjustment system was designed on the gradient index photonic crystals. The focal length range of 1.1374 λ～2.6264 λ could be adjusted without changing the structure of gradient index photonic crystals. Meanwhile, the half-width of the focal spot was less than 0.4 λ.

Spatiotemporal optical vortices (STOVs) carrying transverse orbital angular momentum are a new type of optical pulse wave packet, and attract more and more attention from researchers around the world. In this paper, we present a method of generating linearly polarized STOVs with controllable polarization states on the focal plane of a high numerical aperture lens. The incident wave packet is pre-split to overcome the spatiotemporal astigmatism caused by the focusing lens to the STOV. The three dimensional spatiotemporal distributions of the highly confined STOVs with different polarization states are simulated based on Richards Wolf vectorial diffraction theory to analyze their intensity and phase characteristics. The obtained horizontally polarized, vertically polarized and 45° polarized highly confined STOVs manifest the feasibility of the presented method.

The ultrafast carrier and phonon dynamics of SnSe2 thin films grown by chemical vapor deposition are investigated based on a self-built ultrafast pump-probe experimental system. By measuring the carrier relaxation process of the SnSe2 thin films with the variation of pumping energy density, the results showed that the thin films had an ultrafast carrier thermalization process and a composite process on the picosecond to nanosecond time scale. Accompanied by the ultrafast excitation and energy relaxation of photogenerated carriers, the SnSe2 thin films underwent lattice thermalization and generated coherent acoustic phonons of specific frequencies. The properties of the coherent acoustic phonons generated by the SnSe2 thin films were revealed by analyzing the variation of the acoustic phonon oscillation signal with the pumping energy density. The results of this study provide reference value for the study of the application of SnSe2 thin films in the field of optoelectronic devices.

Increasing the energy of terahertz pulses has been one of the research hotspots of ultrafast optics in recent years. In this paper, based on the numerical model of terahertz wave generated by two-color laser plasma filament in air, in the range of tunneling ionization, we analyze in detail the optimal parameter combination of terahertz wave generated by two-color laser field and the physical mechanism of its change, so as to obtain the strongest terahertz wave radiation energy. We analyze its physical mechanism. The electric field of the combination of two-color laser fields is asymmetric, and the rapid oscillation enhances the acceleration process of electrons, resulting in larger electron number density and stronger cumulative net current along the plasma filament. When the electron density and net current increase, the single point terahertz radiation is stronger, and the terahertz waves radiated at each point of plasma filament are coherently superimposed, so a stronger terahertz wave energy is obtained in the far field. These research results provide a detailed parameter analysis and theoretical basis for enhancing the radiation energy of THz wave under different laser generation conditions, and focus on the influence of unusual wavelength combination and different relative phases on the generation of terahertz wave by laser wire drawing, which is of great significance for greatly enhancing the radiation efficiency of THz in the future.

In order to further explore the new detection technology of terahertz based on cesium Rydberg atom, we studied the radiation lifetime after atomic transition and the sensitivity of system noise limitation under different transition modes (S1/2→P3/2、D5/2→P1/2、D5/2→P3/2) using simulation under four-level Rydberg atomic model. The simulation results show that the atomic radiation lifetime after transition increases with the increase of its energy level principal quantum number. Among the three transition modes of the model, the atomic radiation lifetime of S1/2→P3/2 is shorter than the other two transition modes. For the shot noise limited sensitivity, the sensitivity value of D5/2 →P1/2 transition mode is the smallest, that is, the detection sensitivity of the system will be the highest in this transition mode. This conclusion provides a reference for the Redburg atomic terahertz detection technology and lays a foundation for weak signal detection in the field of biology and materials.

To address the challenges of complex process and poor substrate adaptability in current low-dimensional material transfer schemes, a fixed-site transfer method based on flexible polymer film polydimethylsiloxane (PDMS) is proposed in this paper. The deformation of PDMS flexible film is the basis for its close adhesion to different substrates. For different target substrates, only the corresponding substrate micro-adjustment system cover plate need to be replaced, and in combination with the three-dimensional displacement mechanical system, the universal fixed-point transfer of one-dimensional and two-dimensional materials is realized. This method avoid the strict conditions of vacuum adsorption and substrate heating during the transfer process, which effectively reduce the difficulty of the fixed-point transfer of low-dimensional materials and improve the transfer stability and versatility. In addition, this method also enable the construction of homogeneous junctions or other vertical structures of low-dimensional materials, thus greatly improving the structural richness of low-dimensional materials.

The sensibility of a waveguide evanescent wave sensor is limited by its evanescent wave intensity. To improve the sensibility of the sensor, the evanescent wave intensity of the waveguide was enhanced by designing a high-refractive-index resin layer on the surface of the waveguide. To optimize the layer thickness, the relationship between the evanescent wave ratios and the layer thicknesses under different refractive index values was studied. A laser-induced waveguide self-written technique was utilized to fabricate an evanescent wave sensor by coating a layer on the waveguide with refractive index of 1.6 and a thickness of 300 nm, respectively. The UV-Vis spectral measurement results show that after the layer coating, the absorption detection limit of Rhodamine B aqueous solution is increased to 1×10–9 g/mL, which is 10 times enhanced than that of the uncoated sensor. The sensor has the merits of low cost, small size, simple fabrication and high sensitivity, which has broad application prospects in various fields.

As one of the key components of an optical system, the processing quality of the lens greatly affects the performance of the optical system. The variation of the lens' center thickness has the most significant impact on the overall imaging quality of the optical system. The existing non-contact and contact measurement equipment has some shortcomings. Therefore, this paper proposes a diameter adaptive method for measuring the center thickness of a lens. Based on this method, a set of lens center thickness measurement device was designed and built. The measurement accuracy comparison and the repeatability measurement test are carried out. The results show that the error of the measurement device studied in this paper is comparable to the error of the measurement device used in the production line, which meets the detection requirements of optical lenses. The device has the advantages of simple and reliable structure, convenient operation, high measurement accuracy, and saving the production cost of optical lenses, and has been used in production lines.

The random walk model (RWM) can accurately predict the jamming probability of frictionless granular system in a silo. However, the applicability of this theoretical model for systems with friction remains unclear. In this study, a measuring device based on array CCD cameras is built. The characteristic parameters of jamming arch are measured by image method. It is found that the random walk model can accurately predict the silo jamming probability when the mean angle between two adjacent granules is negatively linear with the granular position on the jamming arch and the mass discharge rate is greater than 8.3 g/s. The experimental results extend the application scope of the RWM and provide a reference for the control process of silo devices in industrial production.