We demonstrate a novel all-fiber laser generating cylindrical vector beams with high slope efficiency and low threshold by introducing a long-period fiber grating into the laser cavity. Highly efficient mode conversion is realized by an LPFG at $\sim 1548\mathrm{nm}$. Mode selection and spectrum filtering are achieved in combination with a two-mode fiber Bragg grating (TM-FBG). The fiber laser operates at a single wavelength of 1547.95 nm with a 30 dB linewidth of less than 0.18 nm and a side-mode suppression ratio (SMSR) of more than 56 dB. The lasing threshold and slope efficiency of the laser are 24.5 mW and 35.41%, respectively. The output power is 72 mW with an absorbed pump power of 225 mW. The variation of slope efficiency with respect to the reflectivity of the TM-FBG is investigated. Through adjusting the intra-cavity polarization controller, high-purity radially and azimuthally polarized beams are both obtained.

Spintronic thin films were shown to be promising high-performance broadband terahertz (THz) emitters. For spintronic ferromagnet/heavy metal heterostructures, THz emission arises from three mechanisms: the magnetic dipolar radiation due to the ultrafast demagnetization, the transient current radiation due to spin-charge conversion, and anomalous Hall effect. Here, we demonstrate that the three mechanisms show distinct dependences on the thickness of the ferromagnetic layer. With the insertion of an ultrathin ${\mathrm{Al}}_2{\mathrm{O}}_3$ layer between the ferromagnetic and heavy metal layer, the spin-charge conversion is suppressed when the ${\mathrm{Al}}_2{\mathrm{O}}_3$ thickness exceeds 1 nm. Our results agree with the theoretical predictions based on a simple spin-diffusion model.

This paper proposes a novel infrared camera array guidance system with capability to track and provide real time position and speed of a fixed-wing Unmanned air vehicle (UAV) during a landing process. The system mainly include three novel parts: (1) Infrared camera array and near infrared laser lamp based cooperative long range optical imaging module; (2) Large scale outdoor camera array calibration module; and (3) Laser marker detection and 3D tracking module. Extensive automatic landing experiments with fixed-wing flight demonstrate that our infrared camera array system has the unique ability to guide the UAV landing safely and accurately in real time. Moreover, the measurement and control distance of our system is more than 1000 m. The experimental results also demonstrate that our system can be used for UAV automatic accurate landing in Global Position System (GPS)-denied environments.

With features of fast and energy-efficient data writing, all-optical helicity-dependent switching (AO-HDS) has emerged as a competitive technology to satisfy the demand for the next-generation volume data storage. Unfortunately, to switch the magnetizations in different positions of the magnetic-optic film, the laser beam, the objective lens, or the magnetic recording film should be moved, limiting the advantage of AO-HDS in fast data writing. To achieve on-the-fly magnetization switching, the induced magnetization should be fully controllable. In this Letter, by focusing an azimuthally polarized vortex beam (APVB) and introducing an additional phase, a feasible strategy constructing subwavelength light-induced pure longitudinal multi-magnetization spots is proposed. In addition, the position of the multi-magnetization spots can be dynamically controlled. The distributions of the focused APVBs with different orbital angular momentum, and the induced magnetizations are surveyed. We believe that this is a practical and flexible three-dimensional magnetic recording technique with dynamic control of the recording position.

Spintronic thin films are considered as one of the promising terahertz (THz) source candidates, owing to their high performance and low cost. Much effort has been made to achieve spintronic THz sources with broadband and high conversion efficiency. However, the development of spintronic THz emitters with good compatibility, low cost, and miniaturized technology still faces many challenges. Therefore, it is urgent to extend commercial and portable spintronic THz emitters to satisfy many practical applications. Herein, we design a new generation of spintronic THz emitters composed of an alternating electromagnet and a miniaturized electronic controller. Not only can this new type of spintronic THz emitter largely simplify the ancillary equipment for spintronic sources, it also has a twice larger THz signal compared to the traditional THz time-domain spectroscopy systems with a mechanical chopper. Experimental results and theoretical calculations for electromagnetic coils show that our design can stably generate THz signals that are independent of the frequency and magnetic field of alternating signals. As the spin thin film is optimized, a magnetic field as low as 75 G satisfies the requirement for high performance THz emission. Hence, not only is the efficiency of the pump power enhanced, but also the driving current in the electromagnet is decreased. We believe that it has a wide range of applications and profound implications in THz technology based on spintronic emitters in the future.

Spectral fingerprint and terahertz (THz) field-induced carrier dynamics demands the exploration of broadband and intense THz signal sources. Spintronic THz emitters (STEs), with high stability, a low cost, and an ultrabroad bandwidth, have been a hot topic in the field of THz sources. One of the main barriers to their practical application is lack of an STE with strong radiation intensity. Here, through the combination of optical physics and ultrafast photonics, the Tamm plasmon coupling (TPC) facilitating THz radiation is realized between spin THz thin films and photonic crystal structures. Simulation results show that the spectral absorptance can be increased from 36.8% to 94.3% for spin THz thin films with TPC. This coupling with narrowband resonance not only improves the optical-to-spin conversion efficiency, but also guarantees THz transmission with a negligible loss (∼4%) for the photonic crystal structure. According to the simulation, we prepared this structure successfully and experimentally realized a 264% THz radiation enhancement. Furthermore, the spin THz thin films with TPC exhibited invariant absorptivity under different polarization modes of the pump beam and weakening confinement on an obliquely incident pump laser. This approach is easy to implement and offers possibilities to overcome compatibility issues between the optical structure design and low energy consumption for ultrafast THz opto-spintronics and other similar devices.