Last decade has witnessed a rapid development of the generation of terahertz (THz) vortex beams as well as their wide applications, mainly due to their unique combination characteristics of regular THz radiation and orbital angular momentum (OAM). Here we have reviewed the ways to generate THz vortex beams by two representative scenarios, i.e., THz wavefront modulation via specific devices, and direct excitation of the helicity of THz vortex beams. The former is similar to those wavefront engineering devices in the optical and infrared (IR) domain, but just with suitable THz materials, while the latter is newly-developed in THz regime and some of the physical mechanisms still have not been explained explicitly enough though, which would provide both challenges and opportunities for THz vortex beam generation. As for their applications, thanks to the recent development of THz optics and singular optics, THz vortex beams have potentials to open doors towards a myriad of practice applications in many fields. Besides, some representative potential applications are evaluated such as THz wireless communication, THz super-resolution imaging, manipulating chiral matters, accelerating electron bunches, and detecting astrophysical sources.

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In this paper, AuNRs colloids with SPR L located at ~810 nm and ~1100 nm were synthesized using an improved seed method. Based on the NIR lasers available, photothermal conversion of AuNRs were systematically studied compared with that of water. Under low power irradiation, the highest temperature is obtained when the SPR L wavelength of AuNRs is equal to the laser wavelength, and temperature of colloid increases from ~20˚C to ~65˚C. With increasing laser power (such as 6 W), the AuNRs colloid boils within a few minutes, and nanorods undergo a shape deformation from rod to spherical particle and even fusion, and the SPR L disappears. For further investigation, the obtained AuNRs were coated with SiO 2 shell to form a core-shell nanostructure (Au@SiO 2). The surface coating can be used not only in keeping the stability of AuNRs for further treatment, but also in increasing plasmonic property and biocompatibility. This work will be useful for designing plasmonic photothermal properties and further applications in nanomedicine.

Neuropathic pain is caused by somatosensory nervous system disorder which happens in patients with different diseases. Akt3 regulates innate immune function and plays a role in neuropathic pain pathogenesis in rats. MiR‐20b‐5p is a microRNA which has been suggested to inhibit Akt3 expression through directly targeting Akt3 mRNA. This research focused on miR‐20b‐5p function in neuropathic pain by Akt3 expression inhibition. Chronic constriction injury (CCI) was employed to induce neuropathic pain in rats. Paw withdrawal thresholds and paw withdrawal latency were examined to show neuropathic pain development. Expression levels of relative genes or microRNA were checked using qRT‐PCR and western blot. Inflammation cytokine levels were measured by enzyme‐linked immunosorbent assay kits. In CCI rat model, miR‐20b‐5p level was declined and Akt3 mRNA level was upregulated. MiR‐20b‐5p mimics suppressed the enhanced neuropathic pain, neuroinflammation, and Akt3 expression. MiR‐20b‐5p directly targeted Akt3 mRNA and downregulated the Akt3 expression in rat primary microglial cells. MiR‐20b‐5p inhibitory function in neuropathic pain was suppressed by the upregulation of Akt3 expression. This research illustrated that miR‐20b‐5p alleviated neuropathic pain through the inhibition of Akt3 expression in CCI rat model.

We theoretically and numerically investigate the generation and evolution of different pulsed terahertz (THz) singular beams with an ultrabroad bandwidth (0.1–40 THz) in long gas-plasma filaments induced by a shaped two-color laser field, i.e., a vortex fundamental pulse (ω0) and a Gaussian second harmonic pulse (2ω0). Based on the unidirectional propagation model under group-velocity moving reference frame, the simulating results demonstrate that three different THz singular beams, including the THz necklace beams with a π-stepwise phase profile, the THz angular accelerating vortex beams (AAVBs) with nonlinear phase profile, and the THz vortex beams with linear phase profile, are generated. The THz necklace beams are generated first at millimeter-scale length. Then, with the increase of the filament length, THz AAVBs and THz vortex beams appear in turn almost periodically. Our calculations confirm that all these different THz singular beams result from the coherent superposition of the two collinear THz vortex beams with variable relative amplitudes and conjugated topological charges (TCs), i.e., +2 and −2. These two THz vortex beams could come from the two four-wave mixing (FWM) processes, respectively, i.e., ω0+ω0−2ω0→ωTHz and –(ω0+ω0) + 2ω0→ωTHz. The evolution of the different THz singular beams depends on the combined effect of the pump ω0−2ω0 time delay and the separate, periodical, and helical plasma channels. And the TC sign of the generated THz singular beams can be easily controlled by changing the sign of the ω0−2ω0 time delay. We believe that these results will deepen the understanding of the THz singular beam generation mechanism and orbital angular momentum (OAM) conversion in laser induced gas-filamentation.