In this paper, a broadband and thermally switchable reflective metasurface based on InSb Z-shape resonator (ZSR) structure was proposed for the vortex beam generation in terahertz (THz) region. Numerical simulation results indicate that the operation frequency range and efficiency will be basically unchanged when the external environment temperature increases from 300 K to 340 K, but gradually decreased when the temperature decreases from 300 K to 240 K. More specifically, the proposed InSb metasurface can transform the normal incident circular-polarization (CP) wave to its orthogonal component with conversion coefficient over 0.8 from 0.65 THz to 1.66 THz (relative bandwidth of 87.4%) after reflection when the temperature is changed from 300 K to 340 K. However, the bandwidth will be narrowed and conversion coefficient will be limited with the temperature decreases from 300 K to 240 K. The full 2π phase shift could be obtained at operation frequency by rotating the InSb ZSR structure along the wave propagation direction. Taking advantages of the above characteristics, the reflective THz vortex beams carrying orbital angular momentum (OAM) with topological charge of l = ±1, ±2, and ±3 at the temperature of 300 K over a broadband range can be achieved. In addition, thermal switchable effect of the vortex beams with topological charge of l = 2 at three different frequencies also can be observed. The further numerical results also indicate that the generated reflective THz vortex beams have high mode purity by the designed InSb metasurface. Our work provides a potentially efficient method for the development and integration of the broadband and switchable wavefront controlling devices. 

Broadband and thermally switchable reflective metasurface based on Z-shape InSb for terahertz vortex beam generation

Broadband transparent terahertz vortex beam generator based on thermally tunable geometric metasurface

In this paper, an all-metal metasurface (MS), which can achieve high-efficient reflective circular-polarization conversion and multifunctional terahertz (THz) wavefront manipulation in an ultra-broadband frequency range, is proposed and investigated theoretically. The proposed all-metal MS consists of the periodic array of a gold vertical-split-ring (VSR) structure adhered on gold substrate. Numerical simulation results indicate that the proposed MS structure can convert the incident circular-polarization (CP) wave into its orthogonal component after reflection with a conversion coefficient over 95% from 0.8 to 1.65 THz (relative bandwidth of 68.3%). The full 2π phase shift of the proposed MS in this frequency range can be obtained by changing the rotation angle of the VSR structure along the wave propagation direction. As proof of concept for the multifunctional wavefront manipulation, anomalous reflection, reflective planar focusing, and vortex beam generation are numerically demonstrated based on the Pancharatnam-Berry (PB) phase principle. Our work can provide an effective method of enhancing the performance of reflective-type all-metal MS and show endless potential in wavefront manipulation and communication applications in THz and even optical region. 

Ultra-broadband high-efficiency circular polarization conversion and terahertz wavefront manipulation based on an all-metallic reflective metasurface

A transmission‐type metasurface (MS) based on the combined geometric and transmission phase is proposed and investigated here numerically, which can achieve independently manipulation of the circular polarization (CP) and linear polarization (LP) wavefront at terahertz (THz) region. The unit‐cell of the proposed MS is composed of the dielectric substrate sandwiched with the bilayered inner centrosymmetric‐notched‐elliptic (CNE), outer C‐shaped, and single‐split‐ring (SSR) structures. The proposed MS can convert the normal incident LP wave to its orthogonal one at the lower frequency (f1 = 0.68 THz) after transmission and left‐handed circular polarization to the transmitted right‐handed circular polarization wave or vice versa at the higher frequency (f2 = 1.34 THz). The full 2π phase shifts of the both transmitted LP and CP waves can be realized independently and simultaneously by varying the opening and orientation angles of the outer SSR structure based on the transmission phase and the orientation angle of the inner CNE structure based on geometric phase, respectively. As proofs of concept, anomalous refraction, planar focusing, and vortex beam generation for both LP and CP waves are demonstrated numerically. These findings show great potential applications in imaging and communication systems, providing new possibilities to develop multifunctional THz device for both LP and CP waves.

Terahertz Transmission‐Type Metasurface for the Linear and Circular Polarization Wavefront Manipulation

Design of broadband terahertz vector and vortex beams: I. Review of materials and Components. Light: Abstract In this paper, we review the existing approaches for vortex and vector beam shaping and generation in the terahertz frequency range. The particular focus of this review is on the possibility of homogeneous topological charge formation in the ultra-wide spectral interval inherent to ultrashort terahertz pulses. We review the available materials and components, analyse proposed and potentially possible solutions for broadband terahertz vortex and vector beam shaping, compare all developed approaches, and put forward a unified concept for constructing passive shapers of such beams from the existing component base.

Design of broadband terahertz vector and vortex beams: I. Review of materials and components

Orbital angular momentum (OAM) is an effective way to increase wireless communication capacity. The existing OAM mainly focuses on the optical and microwave frequency domain. In this letter, a reflective metasurface is proposed to generate an OAM vortex wave beam in the terahertz region with different topological charges. Under illumination of a circular polarized wave, the proposed metasurface generates the deflected OAM vortex wave beam with topological charges of l=±1 and l=±2 at a wide terahertz band from 0.3THz to 0.45THz. The OAM beam has a high mode purity that is larger than 90% at 0.4THz. Both theoretical prediction and simulated results verify that the designed metasurface can achieve a terahertz vortex wave beam with different OAM topological charges.

Simple terahertz vortex beam generator based on reflective metasurfaces.

Objective: To compare the difference between the built-in and external reference electrode of microwire electrode array in the process of recording rat brain neuron firings, optimizing the production and embedding of the microwire electrode array, and providing a more affordable and excellent media tool for multi-channel electrophysiological real-time recording system. Methods: A 16 channel microwire electrode array was made by using nickel chromium alloy wires, circuit board, electrode pin and ground wires (silver wires). The reference electrode of the microwire electrode array was built-in (the reference electrode and electrode array were arranged in parallel) or external (the reference electrode and ground wire were welded at both ends of one side of the electrode), and the difference between the two electrodes was observed and compared in recording neuronal discharges in ACC brain area of rats. Experimental rats were divided into built-in group and external group, n=8-9. The test indicators included signal-to-noise ratio (n=8), discharge amplitude (n=380) and discharge frequency (n=54). Results: The microwire electrode array with both built-in and external reference electrodes successfully recorded the electrical signals of neurons in the ACC brain region of rats. Compared with the external group, the electrical signals of neurons in built-in group had the advantages of a higher signal-to-noise ratio (P＜0.05), a smaller amplitude of background signals and less noise interference, and a larger discharge amplitude(P＜0.05); there was no significant difference in spike discharge frequency recorded by these two types of electrodes (P＞0.05). Conclusion: When recording the electrical activity of neurons in the ACC brain region of rats, the microwire electrode array with built-in reference electrode recorded electrical signals with higher signal-to-noise ratio and larger discharge amplitude, providing a more reliable tool for multi-channel electrophysiology technology.

[A comparative study of microwire electrode array with built-in and external reference electrodes].

Objective: To establish an improved method of separating microglia from aged rats and to observe the biological characteristics of spinal microglia of aged rats. Methods: Young SD rats (2 months) were used as control group. Single cell suspension of rat microglia were prepared by trypsin, trypsin substitutes or mechanical net rubbing method. Then, by assessing the purity and survival rate of cells, and observing the morphological characteristics and analyzing the inflammatory functional characteristics, we optimized the isolation and purification method of microglia from aged rats (20 months old) , and observed the functional characteristics of spinal microglia in aged rats. Results: The survival rate of cells digested by pancreatic enzyme was low(young rats 83%, aged rats 60%). Although the survival rate of mechanical net rubbing method was higher than that of pancreatic enzyme digest methods (95%), the cell acquisition rate was lower(young rats(0.207±0.020)×106, aged rats(0.243±0.023)×106). Trypsin substitute dissociation combining density gradient centrifugation method was the best way to get abundant, active and higher survival microglia, and the purity reached more than 85%. We used this method to separate microglia from spinal cord of rats. Compared with the young rats, the spinal cord tissue of old rats was larger, the digestive fluid volume was higher, but the digestion time was shorter. Compared with the young rats, the aged rat spinal microglia had larger and rounder cell body, fewer and shorter protrusions, it tended to be activated morphologically, the level of proinflammatory cytokine IL-1β of microglia in aged rats was lower, and the level of antiinflammatory factor IL-10 was higher. Conclusion: The method of trypsin substitute dissociation combined with density gradient centrifugation was successfully established to isolate and purify microglia from spinal cord of rats, the spinal microglia of old rats showed anti-inflammatory phenotype.

[A new method of microglia sorting and functional characteristics of spinal microglia in aged rats].

The present study was aimed to explore the involvement of dopamine D1 receptor of the anterior cingulate cortex (ACC) in the regulation of chronic inflammatory pain-related emotion. On the first day, the rats were acclimated to the environment and the baseline indices were measured. On the second day, the rats were administered with the dopamine D1 receptor antagonist SCH-23390 or agonist SKF38393 in the ACC, and then they were subcutaneously injected with complete Freund's adjuvant (CFA, 0.08 mL) in the left hind paw to establish conditioned place avoidance (CPA) response after pairing with specific environment. On the third day, the CPA response and the firing frequency of ACC neurons were observed synchronously, and the open-field behavior, mechanical pain behavior and paw withdrawal latency (PWL) tests were also observed subsequently. In other experiments, rats were given subcutaneous injection of normal saline (NS) on the left hind paw after SCH-23390 or SKF-38393 was administered in the ACC, and then the same observations were performed. The results showed that: (1) Compared with the control group, the PWL and mechanical pain thresholds of rats injected with CFA on the left hind paw were significantly decreased (P < 0.05); (2) The residence time of rats injected with CFA in the "pain environment" and open field center was significantly shortened (P < 0.05); (3) Pre-injection of antagonist SCH-23390 in ACC (10 μg) alleviated the anxiety-like negative behavior response induced by CFA (P < 0.05) and reversed CFA-induced increases of discharge frequency of ACC neurons (P < 0.05); (4) Pre-injection of agonist SKF-38393 in the ACC (10 μg) induced CPA-like behavioral response in rats injected with NS in the left hind paw, and increased the firing frequency of ACC neurons (P < 0.05); (5) Immunofluorescence detection showed that dopamine D1 receptor and NMDA receptor were co-expressed in the same neuron. These results suggest that inhibition of dopamine D1 receptor in ACC can alleviate the negative emotional response induced by persistent pain.

[Behavioral-electrophysiological observation of the involvement of dopamine D1 receptor of the rat anterior cingulate cortex in the regulation of pain-related emotion].

Li-Na Zhang

Papers

Simple terahertz vortex beam generator based on reflective metasurfaces.

[A comparative study of microwire electrode array with built-in and external reference electrodes].

[A new method of microglia sorting and functional characteristics of spinal microglia in aged rats].

[Behavioral-electrophysiological observation of the involvement of dopamine D1 receptor of the rat anterior cingulate cortex in the regulation of pain-related emotion].