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All-fiber mode-locked laser emitting broadband-spectrum cylindrical vector mode
摘要： We experimentally demonstrate an all-fiber mode-locked laser emitting broadband-spectrum cylindrical vector mode pulse based on nonlinear polarization rotation and long-period fiber grating. In this laser, A few-mode long-period fiber grating with broad bandwidth of 125 nm at 1.0 μm band is utilized as mode converter inside the cavity. A flat-end connector deposited with gold film is used as output coupler offering a wideband reflection. Thus the generation of broadband spectrum cylindrical vector mode is feasible owing to the combination of broadband mode converter and output coupler. Stable mode-locked train is achieved at a repetition rate of 9.83 MHz and pulse duration of 168 ps. The proposed laser oscillates at 1030 nm with a broad spectral width of 5 nm at 3 dB. All four degenerate vector modes in the first group higher-order mode can also be obtained with mode purity higher than 95%. This work may have the potential for generation of high-purity and ultra-fast cylindrical vector beam.
关键词： Cylindrical vector beam,Fiber laser,Broadband spectrum,Mode-locking
更新于2025-09-16 10:30:52
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Design and Fabrication of Dual-Scale Broadband Antireflective Structures on Metal Surfaces by Using Nanosecond and Femtosecond Lasers
摘要： Antire?ective surfaces, with their great potential applications, have attracted tremendous attention and have been the subject of extensive research in recent years. However, due to the signi?cant optical impedance mismatch between a metal surface and free space, it is still a challenging issue to realize ultralow re?ectance on a metal surface. To address this issue, we propose a two-step strategy for constructing antire?ective structures on a Ti-6Al-4V (TC4) surface using nanosecond and femtosecond pulsed lasers in combination. By controlling the parameters of the nanosecond laser, microgrooves are ?rst scratched on the TC4 surface to reduce the interface re?ection. Then, the femtosecond laser is focused onto the sample surface with orthogonal scanning to induce deep air holes and nanoscale structures, which e?ectively enhances the broadband absorption. The antire?ection mechanism of the dual-scale structures is discussed regarding morphological characterization and hemispherical re?ectance measurements. Finally, the modi?ed sample surface covered with micro-nano hybrid structures is characterized by an average re?ectance of 3.1% over the wavelengths ranging from 250 nm to 2250 nm.
关键词： nanosecond laser,broadband spectrum,femtosecond laser,micro-nano hybrid structures,antire?ective surfaces
更新于2025-09-12 10:27:22
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Generation of rogue waves in gyrotrons with high excess over the threshold
摘要： Many physical systems exhibit behavior associated with the emergence of the so-called rogue waves which represent dramatically high-amplitude events that occur with low probability but much more frequently than expected in ordinary wave statistics [1]. For example, in laser physics and optics rogue waves arise in the process of supercontinuum generation and represent pulses of ultra broadband light with extremely high peak power [2]. In this paper within the framework of the average approach and in direct 3D PIC (particle-in-cell) simulations we demonstrate that rogue waves can also appear in gyrotrons operating with high excess over the threshold. The mechanism of extreme spikes formation is related to simultaneous cyclotron interaction of a gyrating electron beam with forward and backward waves near the waveguide cutoff frequency as well as with the longitudinal deceleration of electrons. From the practical point of view, experimental observation of the rogue waves generation in gyrotrons can be interesting as a method for production of high-power millimeter-wave radiation with an ultra broadband spectrum. The required exceeding over the threshold can be achieved for routine parameters of the driving electron beams formed by the magnetron-injection guns due to operation at the lowest modes of microwave cavities.
关键词： high-power millimeter-wave radiation,rogue waves,gyrotrons,ultra broadband spectrum
更新于2025-09-10 09:29:36
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Current‐Enhanced Broadband THz Emission from Spintronic Devices
摘要： An ultra-broadband terahertz (THz) emitter covering a wide range of frequencies from 0.1 to 10 THz is highly desired for spectroscopy applications. So far, spintronic THz emitters have been proven as one class of efficient THz sources with a broadband spectrum while the performance in the lower THz frequency range (0.1–0.5 THz) limits its applications. In this work, a novel concept of a current-enhanced broad spectrum from spintronic THz emitters combined with semiconductor materials is demonstrated. A 2–3 order enhancement of the THz signals in a lower THz frequency range (0.1–0.5 THz) is observed, in addition to a comparable performance at higher frequencies from this hybrid emitter. With a bias current, there is a photoconduction contribution from semiconductor materials, which can be constructively interfered with the THz signals generated from the magnetic heterostructures driven by the inverse spin Hall effect (ISHE). These findings push forward the utilization of metallic heterostructure-based THz emitters on the ultra-broadband THz emission spectroscopy.
关键词： spintronic devices,broadband spectrum,photoconduction,terahertz emitters
更新于2025-09-04 15:30:14