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Doubly passively Q-switched Tm:YAP laser with MoS2 and WS2 saturable absorbers at 2 μm
摘要： By simultaneously inserting MoS2 and WS2 saturable absorbers (SAs) into laser resonator, a doubly passively Q-switched Tm:YAP laser at 2 μm was realized. Measurements of the average output power, the pulse width and the pulse repetition frequency (RF) have been undertaken. In comparison to singly Q-switched laser using MoS2 or WS2, the doubly Q-switched laser using both MoS2 and WS2 can generate more stable pulse trains with shorter pulse width and higher peak power. At the absorbed pump power of 6.04 W, the maximum peak power of 22.4 W and the shortest pulse width of 249.4 ns were obtained. While for singly Q-switched laser using MoS2 or WS2, they were 10.7 W, 528.4 ns and 14.4 W, 458.8 ns. The experimental results hit at a conclusion that the doubly passively Q-switched operation is an e?cient way to compress the pulse width, improve the peak power and enhance the stability of pulse trains at 2 μm waveband laser.
关键词： Pulse width,Peak power,Doubly passively Q-switch,Two-dimensional material
更新于2025-09-19 17:13:59
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Graphene Photonics || Electronic Properties
摘要： The ?ow of free charge carriers, i.e., electrons in the conduction band or holes in the valence band, in a semiconductor that is subject to an electric ?eld is accelerated by the electric field but is hindered by scattering events. In a semiconductor, free carriers accelerate in the presence of an electric field. The randomly distributed scattering centers, such as impurities and defects, act as a counter force that decelerates and de?ects the carriers. When the steady state is eventually reached under a constant electric field, a constant ?ow of carriers is achieved. In graphene, by contrast, charge carriers on the Dirac cone have a constant speed and do not accelerate or decelerate in response to the electric field or the scattering centers; instead, the effect of the electric field is rather to align the motion of carriers to the direction of the electric field, and the scattering centers act as a source to disturb this alignment process. This process is well captured by the Boltzmann transport equation, which has successfully described many statistical behaviors of carriers in metals and semiconductors. The purpose of this chapter is to describe the electronic properties of graphene, starting from the Boltzmann transport equation.
关键词： Boltzmann transport equation,charge carriers,electric field,electronic properties,conductivity,scattering events,graphene,two-dimensional material
更新于2025-09-16 10:30:52
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Electron-hole superfluidity controlled by a periodic potential
摘要： We propose controlling an electron-hole super?uid in semiconductor coupled quantum wells and double layers of a two-dimensional (2D) material by an external periodic ?eld. This can be created either by the gates periodically located and attached to the quantum wells or double layers of the 2D material or by the moiré pattern of two twisted layers. The dependence of the electron-hole pairing order parameter on the temperature, the charge carrier density, and the gate parameters is obtained by minimization of the mean-?eld free energy. The second-order phase transition between super?uid and electron-hole plasma, controlled by the external periodic gate ?eld, is analyzed for different parameters.
关键词： mean-?eld free energy,semiconductor coupled quantum wells,electron-hole super?uid,phase transition,external periodic ?eld,two-dimensional material
更新于2025-09-11 14:15:04
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Nucleation promoted synthesis of large-area ReS<sub>2</sub> film for high-speed photodetectors
摘要： Rhenium disulfide (ReS2) is a transition metal dichalcogenide with a layer-independent direct bandgap. Notably, the weak interlayer coupling owing to its T-phase structure enables multi-layer ReS2 to behave similarly to decoupled monolayers. This inherent characteristic makes continuous multi-layer ReS2 film a unique platform for large-area electronic applications. To date, the bulk of work on ReS2 has been conducted using mechanically exfoliated samples or small size flakes (< 1mm2) with no potential for large-scale electronics. A chemical vapor deposition (CVD) synthesis of a large area, continuous ReS2 film directly on a SiO2 substrate is also known to be more challenging compared with that of other 2D materials, such as MoS2 and WS2. This is partly due to its tendency to grow into discrete dendritic structures. In this study, a large-area (> 1 cm2), continuous multilayer ReS2 film is directly synthesized on a SiO2 substrate without any transfer process. The polycrystalline ReS2 film synthesized by this method exhibits one of the fastest photoresponse speeds (0.03 s rise time and 0.025 s decay time) among the reported CVD films. The responsivity Rλ was also the highest among large-area CVD films. The synthesis method for a continuous multilayer ReS2 film is amenable to large-scale integration and will pave the way for practical optoelectronic applications based on 2D layered materials.
关键词： Photodetector,Large-area synthesis,Metal chalcogenides,Chemical vapor deposition,Two-dimensional material,Nucleation promotor
更新于2025-09-11 14:15:04
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Photonic spin Hall effect of monolayer black phosphorus in the Terahertz region
摘要： As a two-dimensional (2D) material, black phosphorus (BP) has attracted significant attention owing to exotic physical properties such as low-energy band gap, high carrier mobility, and strong in-plane anisotropy. The striking in-plane anisotropy is a promising candidate for novel light-matter interaction. Here, we investigate the photonic spin Hall effect (PSHE) on a monolayer of BP. Due to the in-plane anisotropic property of BP, the PSHE is accompanied with Goos-H?nchen and Imbert-Fedorov effects, resulting in an asymmetric spin splitting. The asymmetric spin splitting can be flexibly tuned by the angle between the incident plane and the armchair crystalline direction of BP and by the carrier density via a bias voltage. The centroid displacements of two opposite spin components of the reflected beam along directions parallel and perpendicular to the incident plane can be considered as four independent channels for information processing. The potential application in barcode-encryption is proposed and discussed. These findings provide a deeper insight into the spin-orbit interaction in 2D material and thereby facilitate the development of optoelectronic devices in the Terahertz region.
关键词： in-plane anisotropy,two-dimensional material,black phosphorus,photonic spin Hall effect
更新于2025-09-10 09:29:36