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Type-II heterostructures of <b>α</b> -V <sub/>2</sub> O <sub/>5</sub> nanowires interfaced with cadmium chalcogenide quantum dots: Programmable energetic offsets, ultrafast charge transfer, and photocatalytic hydrogen evolution
摘要： We synthesized a new class of heterostructures by depositing CdS, CdSe, or CdTe quantum dots (QDs) onto α-V2O5 nanowires (NWs) via either successive ionic layer adsorption and reaction (SILAR) or linker-assisted assembly (LAA). SILAR yielded the highest loadings of QDs per NW, whereas LAA enabled better control over the size and properties of QDs. Soft and hard x-ray photoelectron spectroscopy in conjunction with density functional theory calculations revealed that all α-V2O5/QD heterostructures exhibited Type-II band offset energetics, with a staggered gap where the conduction- and valence-band edges of α-V2O5 NWs lie at lower energies (relative to the vacuum level) than their QD counterparts. Transient absorption spectroscopy measurements revealed that the Type-II energetic offsets promoted the ultrafast (10?12–10?11 s) separation of photogenerated electrons and holes across the NW/QD interface to yield long-lived (10?6 s) charge-separated states. Charge-transfer dynamics and charge-recombination time scales varied subtly with the composition of heterostructures and the nature of the NW/QD interface, with both charge separation and recombination occurring more rapidly within SILAR-derived heterostructures. LAA-derived α-V2O5/CdSe heterostructures promoted the photocatalytic reduction of aqueous protons to H2 with a 20-fold or greater enhancement relative to isolated colloidal CdSe QDs or dispersed α-V2O5 NWs. The separation of photoexcited electrons and holes across the NW/QD interface could thus be exploited in redox photocatalysis. In light of their programmable compositions and properties and their Type-II energetics that drive ultrafast charge separation, the α-V2O5/QD heterostructures are a promising new class of photocatalyst architectures ripe for continued exploration.
关键词： α-V2O5 nanowires,cadmium chalcogenide quantum dots,photocatalytic hydrogen evolution,programmable energetic offsets,Type-II heterostructures,ultrafast charge transfer
更新于2025-09-12 10:27:22
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Ultrafast hole extraction from photoexcited colloidal CdSe quantum dots coupled to nitroxide free radicals
摘要： Organic free radicals related to the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical are known as photoluminescence-quenchers when coupled to group II-chalcogenide colloidal quantum dots (QDs), but the mechanism responsible for this phenomenon has so far remained unresolved. Using a combination of time-resolved photoluminescence and transient absorption spectroscopies, we demonstrate that photoexcited colloidal CdSe QDs coupled to 4-amino-TEMPO undergo highly efficient reductive quenching, that is, hole transfer from the valence band of the quantum dot to the organic paramagnetic species. Interestingly, the process is shown to occur on a subpicosecond time scale for bound 4AT; such a large rate constant for the extraction of holes from photoexcited CdSe QD by a molecular species is rare and underlines the potential that TEMPO derivatives can play in mediating efficient redox processes involving colloidal CdSe QDs.
关键词： TEMPO,photoluminescence quenching,ultrafast spectroscopy,colloidal quantum dots,hole transfer
更新于2025-09-12 10:27:22
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Harmonic Mode-Locking in Bidirectional Domain-Wall Soliton Fiber Lasers
摘要： We report on the first experimental observation of passively harmonic mode-locking (HML) in a bidirectional domain-wall dark-soliton fiber laser. The domain-wall solitons (DWSs) are characterized, in which, the strong coupling between the two directions takes great responsibility for the generation. By appropriately altering the polarization state in the cavity, the stable fundamental domain-wall solitons and HML states could be obtained and switched with increasing the pump power. In our experiment, the repetition rate can be tunable from the fundamental mode locking of 2.96 MHz up to eighth-order HML of 23.68 MHz when the pump power is increased from 120 to 542.5 mW. Importantly, this HML operation of dark-pulse DWSs confirms that the DWSs are the intrinsic feature of the mode-locked lasers, as well as the conventional bright solitons. This work could provide a new perspective to the understanding of the formation and transformation of dark solitons, which may also find great potential applications in fiber sensing and future optical communication systems.
关键词： lasers and laser optics,mode-locked lasers,ultrafast photonics,pulse propagation and temporal solitons
更新于2025-09-12 10:27:22
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Plasmonic Hot Hole Transfer in Gold Nanoparticle-decorated Transition Metal Dichalcogenide Nanosheets
摘要： This work studies photogenerated carrier dynamics in gold nanoparticle (AuNP)-decorated mono- to few-layer transition metal dichalcogenide (TMD) nanosheets using transient absorption spectroscopy (TA). TA unveiled the presence of a long-lived photo-induced absorption (PIA) feature in both MoSe2 and WSe2 decorated with covalently bound AuNPs. This long-lived PIA feature emerges only from direct Au interband excitation in AuNP-decorated MoSe2 and WSe2; it does not manifest from intraband excitation nor in AuNP-decorated MoS2 or WS2. Based on x-ray/ultraviolet photoelectron spectroscopy and previous theoretical studies, it is proposed that this PIA signature arises from hot hole transfer from the AuNP to the adjacent TMD, producing a charge-separated state. This suggests charge separation at the metal-semiconductor interface may be used to extend the lifetime of interband excitation generated hot holes. This development could represent an important advance in harnessing plasmonic dissipation pathways to generate long-lived carriers suited for solar-driven light harvesting and catalysis.
关键词： molybdenum diselenide,hot carriers,transient absorption,carrier dynamics,intraband,interband transitions,ultrafast spectroscopy
更新于2025-09-12 10:27:22
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Measurement of electron beam moire fringes with pulsed-dilation framing camera using different lasers
摘要： The electron beam moire fringe (EBMF) is generated by using a pulse-dilation framing camera. Its characteristics are measured via a nanosecond- and a femtosecond-laser. The wavefront curvature radius of the two lasers is calculated based on the measurement of the EMBF rotation angle and this result is discussed in detail. The experiments show that the EBMF rotation angles measure 31.9° and 16.6°, while the wavefront curvature radii are 12.5 mm and 21.1 mm, when the ns-laser and the fs-laser are used, respectively. This study greatly contributes in the development of EBMF-based technologies and proposes novel application directions for the use of pulse-dilation framing cameras.
关键词： Electron beam moire fringe,Ultrafast diagnostic techniques,Wavefront curvature radius,Pulse-Dilation framing camera
更新于2025-09-12 10:27:22
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Generation of high-energy and low-repetition rate hybrid pulses from a passively mode-locked Tm-Ho co-doped laser
摘要： This study presents a passively mode-locked Tm-Ho co-doped ?ber laser at around 1840 nm with a low-repetition rate and high pulse energy. The laser delivers pulses at 93 kHz and produces a pulse energy of 18.5 nJ at 0.55 W pump power when the cavity length is 2.21 km. When the pump power is increased, high order of repetition rate outputs are observed. By a comparison of the spectra at various pump power levels indicates that the laser can be operated at hybrid multi-wavelength soliton mode-locking, depending on the pumping intensity. With the increase in pump power, single-wavelength soliton mode-locking and simultaneous of single- and dual-wavelength soliton mode locking are also observed. Besides, the system produces a laser at 1417 nm, which is induced by two-step absorption and the consequent stimulated emission. The low–repetition rate and high–pulse energy ?ber laser at around 1840 nm has potential applications in sensing, processing, and surgery research.
关键词： Optical ?ber lasers,Mode locked lasers,Ultrafast optics
更新于2025-09-12 10:27:22
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Investigation on geometric precision and surface quality of microholes machined by ultrafast laser
摘要： The geometric precision and surface quality of film cooling holes has significant influence on the cooling efficiency and fatigue life of turbine blades. In this paper, the investigation about fabrication process of film cooling holes on the single crystal superalloy DD6 plate specimen by ultrafast laser is carried out. By comparing three different processing paths, minimum roughness of hole wall could be obtained by concentric circular scanning, which was used in the followed-up experiment. The influence of process parameters on the geometric precision and surface quality of microholes was analyzed, and the physical mechanism was examined. The results show that among several process parameters, focus position has the most significant influence on the microholes geometric precision and surface quality, and that the divergent beam (where the focal plane is above the machined surface) can lead to smaller taper, roundness, and surface roughness. In addition, besides a layer of solidified debris adheres to the inner wall at the hole entrance, the microholes machined by ultrafast lasers have no other defects such as a recast layer, microcrack or heat affected zone.
关键词： Geometric precision,Surface quality,Process parameter,Ultrafast laser,Microhole drilling
更新于2025-09-12 10:27:22
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Novel strategy for ultrafast pulsed laser micromachining of rotational symmetric metallic parts
摘要： Ultra-fast lasers have already been used to machine rotational symmetric metallic parts for several years but did not prevail against much cheaper fiber lasers. The limiting factor up to now is the dynamics of the rotary and linear axes, that are used to move the part underneath the stationary laser beam. Although the quality of the surface machined with ultrafast pulsed laser radiation is better than that machined with fiber laser radiation, an overall economic consideration mostly did not justify the utilization of ultrafast pulse lasers for this kind of application. Therefore, new and innovative concepts are needed to exploit the potential of ultrafast pulse lasers, in particular high repetition rate and the steadily increasing average power. The realization that will be presented uses a high-end galvanometric scanner to move the laser beam at speeds of several ten meters per second across the constantly rotating part. The most important part is the synchronization of the laser, the scanner and the axes.
关键词： efficiency,ultrafast lasers,laser micro machining,synchronization,galvanometric scanner
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Temporal Ghost Imaging with Wavelength Conversion
摘要： Ghost imaging is a non-direct measurement technique that uses the correlation between multiple probing patterns and the integrated signal measured after transmission (or reflection) through an object. [1] The resolution of the technique is determined by the characteristic length scale of the probing patterns fluctuations and/or the resolution with which they can be measured. Originally demonstrated in the spatial domain to reconstruct images of real physical objects, ghost imaging has been recently extended to the time-domain to measure ultrafast signals at telecom wavelengths [2]. In this work, we experimentally demonstrate ultrafast ghost imaging in the time-domain where the correlated intensities have completely different wavelengths. This wavelength-conversion temporal ghost-imaging scheme exploits fully the benefit of ghost imaging opening up new possibilities for ultrafast imaging in spectral regions where sensitive and/or fast detectors are not available and in particular the mid-infrared or THz range.
关键词： temporal domain,mid-infrared,ultrafast imaging,Ghost imaging,wavelength conversion,THz range
更新于2025-09-12 10:27:22
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Precession damping in [Co <sub/>60</sub> Fe <sub/>40</sub> /Pt] <sub/>5</sub> multilayers with varying magnetic homogeneity investigated with femtosecond laser pulses
摘要： We report on the ultrafast magnetization dynamics of [Co60Fe40/Pt]5 multilayers studied with femtosecond laser pulses. The samples were grown at room temperature by DC magnetron sputtering with Ta capping and Pt buffer layers and present the same thickness and perpendicular magnetic anisotropy as determined by vibrating sample magnetometry. Controlled growth rate of the Pt buffer layer modified the anisotropy fields and magnetic domain sizes as measured by magnetic force microscopy (MFM). An estimation of the average magnetic domain sizes was obtained from the profile of the self-correlation transform of the MFM images. For multilayers having an average magnetic domain size of 490 nm, we report a damped precession of the magnetization which decays with a time constant of ～100 ps and which has a frequency which varies from 8.4 GHz to 17.0 GHz as the external field increases from 192 mT to 398 mT. Fitting the precession dynamics with the Landau-Lifshitz-Gilbert equation we evaluated the damping α, which decreases from 0.18 to 0.05 with increasing magnetic domain sizes (127 nm to 490 nm). These α values are higher than for single layers suggesting an enhanced scattering and spin pumping effects from the Pt adjacent layers. In addition, the precession frequency increases from 2.04 GHz to 11.50 GHz as the anisotropy field of the multilayers increases from 6.5 kOe to 13.0 kOe. Finally, a comparative analysis between micromagnetic simulations and MFM images allowed us to determine the exchange stiffness (Aex) in the [Co60Fe40/Pt]5 multilayers.
关键词： exchange stiffness,femtosecond laser pulses,Landau-Lifshitz-Gilbert equation,[Co60Fe40/Pt]5 multilayers,damping,magnetic force microscopy,ultrafast magnetization dynamics,perpendicular magnetic anisotropy
更新于2025-09-12 10:27:22