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Wideband saturable absorption in Metal-organic frameworks (MOFs) for mode-locking Er- and Tm-doped fiber laser
摘要： We fabricate a Metal-organic frameworks (MOFs) Saturable absorber (SA) based on a microfiber. Nonlinear optical absorption of the MOF SA is characterized systmatically. The modulation depth is measured to be 6.57 % and 14.25 % at 1.5 and 2 μm spectral ranges, respectively. We report ultrashort pulse generation in both Er- and Tm-doped fiber lasers by using a same microfiber-based MOF SA, operating 384 fs and 1.3 ps pulse duration at 1563 nm and 1882 nm, respectively. To the best of our knowledge, this is the first report on a MOF based fiber laser at near infrared spectral ranges. Our findings validate the applicability of MOF as a broadband SA for ultrafast photonic applications.
关键词： Ultrafast photonics,Saturable absorber,Metal-organic frameworks,Fiber laser,Nonlinear optical absorption
更新于2025-09-16 10:30:52
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35 fs, all-polarization-maintaining MOPA laser system
摘要： We have experimentally observed ultrashort pulse in a simple, all-polarization-maintaining fiber, master oscillator and power amplifier laser. A semiconductor saturable mirror (SESAM) module is used as the mode locker. The ultrashort pulse exhibits perfect Gaussian spectrum without any fine structure. The 20 dB pulse spectral width is 28 nm, and the pulse duration directly output from the oscillator is 268.6 fs. Via a two-stage amplifier, the pulse spectrum is greatly broadened to 43 nm, and the pulse duration lengths to 0.9 ps. Moreover, after compression, a typical saddle-shaped spectrum appears and the spectral bandwidth broadens to 121 nm; the pulse duration is compressed to ~35 fs with a pulse peak power of 22.79 kW, which is high enough to stimulate a one-octave supercontinuum spectrum. Due to the polarization-maintaining structure and high reliability of SESAM, the whole system exhibits strong environmental stability. Experimental observation reveals that such a fiber laser with a very simple structure exhibits excellent performance, and could be applied in the area of optical frequency comb.
关键词： ultrafast fiber lasers,pulse propagation and temporal solitons,pulse compression
更新于2025-09-16 10:30:52
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Hydrodynamic modeling and time-resolved imaging reflectometry of the ultrafast laser-induced ablation of a thin gold film
摘要： The ablation of thin metal films using ultrafast laser radiation represents a standard processing procedure in laser technology. However, looking closer to the resulting structures, the arising topology deviates strongly from the expected one. Ablation of thin gold films using ultrafast laser radiation with a Gaussian-shaped spatial intensity distribution results in flat topologies. By synergistically combining space and time-resolved reflectometry with expanded two-temperature hydrodynamic modeling, we explain the formation of bulging and rupture of the thin film-surface by the expansion of strongly stretched liquid material due to the induced rarefaction wave propagating towards the substrate. Also, the formation of a flat ablation structure is described by the interplay of two rarefaction waves, one propagating towards the substrate and the other one propagating towards the vacuum boundary, within the completely molten film. The simulated topology agrees excellent with the experimentally observed ablation structure. Besides, all simulated stages of excitation of the gold film, namely electron-phonon non-equilibrium, hydrodynamic expansion, and rupture, are confirmed by space and time-resolved pump-probe reflectometry.
关键词： Imaging reflectometry,Thin film ablation,Femtosecond laser radiation,Two temperature model hydrodynamics (TTMHD),Gold thin film,Ultrafast metrology
更新于2025-09-16 10:30:52
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Heavily doped Semiconductor Colloidal Nanocrystals as Ultra-Broadband Switches for Near Infrared and Mid-Infrared Pulse Lasers
摘要： Heavily self-doped semiconductors can be designed to use for advanced photonics due to both fabrication and functional advantages. Ultrafast response, strong optical nonlinearity, broadband wavelength range and accessibility of integration are major challenges for ultrafast all-optical photonics operating in infrared wavelength range. Here, solution-processed Cu1.8Se semiconductor nanocrystals (NCs) demonstrate ultrafast response (about 360~520 fs), strong optical nonlinearity (as large as -1.4×103 cm GW-1) and broadband (from 800 to 3000 nm) nonlinear optical absorption in the near-infrared and mid-infrared wavelength range. The ultrafast response and larger optical nonlinearity may be triggered by the plasma ground-state bleaching in the strong surface electromagnetic filed. Stable Q-switched lasers in Er-doped fiber laser, Tm-doped fiber laser and Ho/Pr co-doped ZBLAN fiber laser are operated, respectively. These findings indicate that Cu1.8Se NCs are prospective nonlinear materials for ultrafast response and broadband pulse laser.
关键词： semiconductor nanocrystals,ultrafast photonics,optical modulation,superbroadband,nonlinear optical
更新于2025-09-16 10:30:52
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Ultrahigh Stability 3D TI Bi <sub/>2</sub> Se <sub/>3</sub> /MoO <sub/>3</sub> Thin Film Heterojunction Infrared Photodetector at Optical Communication Waveband
摘要： Infrared (IR) detection at 1300–1650 nm (optical communication waveband) is of great significance due to its wide range of applications in commerce and military. Three dimensional (3D) topological insulator (TI) Bi2Se3 is considered a promising candidate toward high-performance IR applications. Nevertheless, the IR devices based on Bi2Se3 thin films are rarely reported. Here, a 3D TI Bi2Se3/MoO3 thin film heterojunction photodetector is shown that possesses ultrahigh responsivity (Ri), external quantum efficiency (EQE), and detectivity (D*) in the broadband spectrum (405–1550 nm). The highest on–off ratio of the optimized device can reach up to 5.32 × 104. Ri, D*, and the EQE can reach 1.6 × 104 A W?1, 5.79 × 1011 cm2 Hz1/2 W?1, and 4.9 × 104% (@ 405 nm), respectively. Surprisingly, the Ri can achieve 2.61 × 103 A W?1 at an optical communication wavelength (@ 1310 nm) with a fast response time (63 μs), which is two orders of magnitude faster than that of other TIs-based devices. In addition, the device demonstrates brilliant long-term (>100 days) environmental stability under environmental conditions without any protective measures. Excellent device photoelectric properties illustrate that the 3D TI/inorganic heterojunction is an appropriate way for manufacturing high-performance photodetectors in the optical communication, military, and imaging fields.
关键词： photodetectors,Bi2Se3 thin films,infrared optical communication wavebands,heterojunction structures,ultrafast response times
更新于2025-09-16 10:30:52
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Visualizing the a??Invisiblea?? Soliton Pulsation in an Ultrafast Laser
摘要： Pulsation is a universal phenomenon that exists in diverse fields. For nonlinear optics, the soliton pulsating behavior can be meaningful for fundamental physics and industrial purpose owing to its fruitful nonlinear dynamics and the possible detrimental effect of instability (or even route to chaos) during pulsating process. Herein, a novel type of soliton pulsation in an ultrafast laser is unveiled. The pulsating behavior features that the soliton experiences periodic peak power variation but with almost invariable pulse energy. This phenomenon is denoted as “invisible soliton pulsation” when referring to the routine diagnostic methods. However, the invisible soliton pulsation can be distinguished by recording the shot-to-shot spectra with real-time spectroscopy technique. It is found that the appearance of the invisible soliton pulsation is sensitive to the pump power level. Moreover, the phenomenon of invisible soliton pulsation is further revealed by numerical simulations. These findings can shed new insights into the complex nonlinear behavior of solitons in dissipative optical systems, and also enrich the performance diagnostic of ultrafast lasers for practical applications.
关键词： soliton dynamics,ultrafast lasers,soliton pulsation
更新于2025-09-16 10:30:52
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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) - Direct Observation of Intracavity Pulse Dynamics in All-Normal Dispersion All-Fiber Oscillator
摘要： Ultrafast science and technology depend strongly on the development of novel ultrafast sources, thus good understanding of nonlinear phenomena in such systems is of essence. In this paper, we present the experimental observation and theoretical analysis of various pulse dynamics in all-normal dispersion cavity producing dissipative soliton pulses. We report the results of an extensive study regarding the Stimulated Raman Scattering (SRS) process, which creates a main upper limitation for the pulse energy achievable from all-normal dispersion fiber oscillators. We report the measurements of real-time, single shot spectra registered using Dispersive Fourier Transform (DFT) technique together with measured averaged spectral phase of the pulses generated from an all-PM-fiber oscillator mode-locked with Nonlinear Optical Loop Mirror (NOLM). It is found that NOLM parameters directly influenced the pulse stability and dynamics. The Yb-doped fiber was used as an active medium and Dissipative Soliton (DS) pulses centered at 1030 nm were generated together with Stokes radiation shifted by 440 cm-1 (centered approximately at 1078 nm) produced in SRS process. The light generated in SRS process was suppressed from round-trip to round-trip by a narrow pass-band spectral filter centered at 1030 nm placed inside the laser cavity. We present the broad experimental study of ultrashort pulse dynamics with strong presence of SRS process. Spectral intensity correlation maps were calculated to describe how the SRS process disturbs the ultrashort pulse during propagation in the cavity (Fig. 1). The intensities of longer wavelengths (1040 – 1050 nm) in the pulse spectrum were destabilized due to the SRS process. In normal dispersion fiber Stokes SRS components have higher group velocity than the pulse spectral components. For positively chirped pulse SRS affects only the leading edge of the pulse which is manifested as negative correlation (Fig. 1(c)). The phenomena of repetitive partial dissipative soliton explosions and bistability of the pulse operation in an all-PM-fiber all-normal dispersion oscillator cavity were investigated as well. The clear signature of bistable operation was the hysteresis of the laser pulse power versus input pump power. Furthermore, we registered significant differences between the measured pulses spectral phases for each case. Another set of measurements was performed to analyze the pulse self-starting dynamics. We present the experimental study and numerical simulations of DS pulse dynamics in an all-normal dispersion all-fiber cavity. The numerical simulations were performed using the standard split-step Fourier-transform method employing the multi-vibrational model of SRS. DS lasers are important pulse sources and an effective platform to investigate the pulse dynamics and nonlinear processes inside the all-fiber cavities.
关键词： spectral intensity correlation maps,Yb-doped fiber,dissipative soliton pulses,Dispersive Fourier Transform,split-step Fourier-transform method,Nonlinear Optical Loop Mirror,Stimulated Raman Scattering,ultrafast science
更新于2025-09-12 10:27:22
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Lithium Distribution in Structured Graphite Anodes Investigated by Laser-Induced Breakdown Spectroscopy
摘要： For the development of thick film graphite electrodes, a 3D battery concept is applied, which significantly improves lithium-ion diffusion kinetics, high-rate capability, and cell lifetime and reduces mechanical tensions. Our current research indicates that 3D architectures of anode materials can prevent cells from capacity fading at high C-rates and improve cell lifespan. For the further research and development of 3D battery concepts, it is important to scientifically understand the influence of laser-generated 3D anode architectures on lithium distribution during charging and discharging at elevated C-rates. Laser-induced breakdown spectroscopy (LIBS) is applied post-mortem for quantitatively studying the lithium concentration profiles within the entire structured and unstructured graphite electrodes. Space-resolved LIBS measurements revealed that less lithium-ion content could be detected in structured electrodes at delithiated state in comparison to unstructured electrodes. This result indicates that 3D architectures established on anode electrodes can accelerate the lithium-ion extraction process and reduce the formation of inactive materials during electrochemical cycling. Furthermore, LIBS measurements showed that at high C-rates, lithium-ion concentration is increased along the contour of laser-generated structures indicating enhanced lithium-ion diffusion kinetics for 3D anode materials. This result is correlated with significantly increased capacity retention. Moreover, the lithium-ion distribution profiles provide meaningful information about optimizing the electrode architecture with respect to film thickness, pitch distance, and battery usage scenario.
关键词： laser-induced breakdown spectroscopy,3D battery,lithium-ion battery,ultrafast laser ablation,graphite anode
更新于2025-09-12 10:27:22
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Hole Transfer Originating from Weakly Bound Exciton Dissociation in Acceptor–Donor–Acceptor Nonfullerene Organic Solar Cells
摘要： The underlying hole-transfer mechanism in high-efficiency OSC bulk heterojunctions based on acceptor?donor?acceptor (A?D?A) nonfullerene acceptors (NFAs) remains unclear. Herein, we study the hole-transfer process between copolymer donor J91 and five A?D?A NFAs with different highest occupied molecular orbital energy offsets (ΔEH) (0.05?0.42 eV) via ultrafast optical spectroscopies. Transient absorption spectra reveal a rapid hole-transfer rate with small ΔEH, suggesting that a large energy offset is not required to overcome the exciton binding energy. Capacitance?frequency spectra and time-resolved photoluminescence spectra confirm the delocalization of an A?D?A-structured acceptor exciton with weak binding energy. Relative to the hole-transfer rate, hole-transfer efficiency is the key factor affecting device performance. We propose that holes primarily stem from weakly bound acceptor exciton dissociation, revealing a new insight into the hole-transfer process in A?D?A NFA-based OSCs.
关键词： hole-transfer mechanism,organic solar cells,exciton dissociation,ultrafast optical spectroscopies,nonfullerene acceptors
更新于2025-09-12 10:27:22
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Ultrafast Plasmonic Optical Switching Structures and Devices
摘要： Plasmonic structures possess rich physics related to the sensitivity of plasmon resonance to the change in the environmental dielectric constant, the enhanced light scattering and optical extinction, and the local field enhancement enabled strong light-matter interactions, which have been applied in refractive-index sensors, optical feedback in various micro- or nano-cavity lasers, surface enhanced Raman scattering spectroscopy, and high-sensitivity molecular detection. However, ultrafast optical response is another important aspect of plasmons, which can be utilized to achieve switching of optical signals in different spectral bands. These optical switching designs are very important for applications in optical logic circuits and optical communication system. In this review, we summarize a series of reports on ultrafast plasmonic optical switches, where we focus our discussions on the structural and device designs, instead of on their physics. By categorizing the designs of optical switches into different groups by their featured performances, we intend to propose the development trend and the commonly interested mechanisms of such ultrafast optical switches. We hope this review will supply helpful concepts and technical approaches for further development and new applications of ultrafast optical switching devices.
关键词： plasmonic device,metal oxides,plasmonic nanostructures,ultrafast optical switching,noble metals,surface plasmon polariton,hybrid plasmons,2D materials
更新于2025-09-12 10:27:22