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- 摘要
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Intraband Ultrafast Terahertz Conductivity Dynamics in Graphene
摘要： The cooling mechanism is crucial for nanoelectronics, which determines the response time limited for the devices. The cooling process after optical pump in graphene, which is a well-known material with ultrahigh carrier mobility, is therefore an urgent research topic. Ultrafast thermalization and relaxation process in a monolayer graphene film grown on a quartz substrate is investigated by femtosecond laser pump, terahertz probe induced negative technique. A typical photo found, and the electron-phonon-impurity supercollision process is determined to about 2.8 picosecond at different pump photon energy and pump fluence. The competition between the impurity supercollision and the interband-intraband scattering in graphene could give new insight into the design of the application of graphene photonic devices.
关键词： ultrafast dynamics,cooling mechanism,electron-phonon-impurity supercollision,terahertz conductivity,graphene
更新于2025-09-16 10:30:52
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Accelerator for Ultrafast Laser Serial Production
摘要： The world of serial applications has long been denied the possibility of ablation processes with ultrafast pulsed laser radiation due to high investment costs and low ablation rates. Nowadays, process scaling with advanced beam shaping technologies make use of the available high laser powers and therefore opens up possibilities for serial processing of individual components. But the exclusive focus on the main time of laser processing is not enough for a production system. Only the combined operation of handling systems, measurement technology, and process automation allow the ultrafast laser technology to spread further into volume markets.
关键词： Production Data Acquisition,Process Automation,Ultrafast Laser Machining,Beam Shaping,Condition Monitoring
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) - Towards Near-Field Coupling of Surface Plasmon Polaritons across Few-Nanometer Gaps between two Laterally Tapered Gold Waveguides
摘要： Nanofocusing of light in combination with an efficient energy transfer of metallic nanostructures is a key task towards ultrafast, all-optical switching on the nanoscale. A possible realization of such a device is based on two tapered plasmonic nanostructures separated by a few-nanometer gap, in which information transport is controlled via strong coupling of the electromagnetic near-field and excitonic molecules in the gap region of the waveguides. The fabrication of such mesoscopic nanostructures that can concentrate free-propagating light to few-nanometers dimensions remains challenging due to the desired nanometer precision in the gap region. Here, we report on the fabrication of a plasmonic nanostructures consisting of a pair of both striped and tapered waveguides in 200 nm thick Au films with gap sizes and radii of curvature down to 11 nm using a Focused Ion Beam-based “Sketch and Peel” lithography process. Curved focused-ion beam written gratings in the waveguides enable the in- and out-coupling and focusing of surface plasmon polaritons into the nanostructure. The propagation of these SPPs is afterwards monitored using far-field confocal microscopy. We find a relatively constant transmission of light for large gap sizes, accompanied by a drastically increase for gap sizes below 20 nm. This increase for small gap sizes can be approximated best by fitting an exponential decay with a decay length of 8 nm suggesting a significant energy transport through near-field coupling of the two waveguides. These experimental findings are in accordance to finite element method and finite difference time domain calculations that show a strong localization of the electric field in the gap region of the two waveguides. The profound electric field strength and the spatial confinement of the electric fields suggest such plasmonic waveguides as prototypical structures for probing the strong coupling between propagating surface plasmon polaritons in adjacent, however separated plasmonic waveguides on one hand and between SPP waves and single quantum emitters that are placed in the gap region of the waveguides on the other hand. The realization of such coupling could enable the ultrafast, remote switching on the nanoscale.
关键词： ultrafast switching,nanofocusing,near-field coupling,surface plasmon polaritons,plasmonic nanostructures
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) - Ultrafast Extreme-Ultraviolet Photoemission Spectroscopy at 18.4 MHz
摘要： In the past two decades, attosecond science has led to important insights into ultrafast electron dynamics. Whilst extreme-ultraviolet (XUV) photon flux attained from high harmonic generation (HHG) has increased significantly over this time, space-charge effects limit the maximum allowable number of photons per pulse for many attosecond experiments, especially in multidimensional – i.e., either angularly (ARPES) or spatially (PEEM) resolved – photoelectron spectroscopy (PES) on solids [1,2]. To allow for higher average flux without increasing space-charge impairments, HHG sources at higher repetition rates are needed. We combine a fibre-based ytterbium amplifier system with 4.5-μJ, 40-fs and 1030-nm pulses at 18.4 MHz repetition rate with intra-cavity HHG with an enhancement of 35 (Fig. 1a). Geometric output coupling through a pierced mirror affords high photon energies of 25-60 eV at a flux of 9×1012 XUV photons per second [3], which is unprecedented at this photon energy and MHz repetition rates. The HHG beam is focused on a tungsten target and the generated photoelectrons are detected by an angle-resolving time-of-flight (ToF) spectrometer. Simultaneous stabilization of cavity length and oscillator repetition rate result in excellent intensity stability of the system and enable long-term measurements with three orders of magnitude less integration time at equal space charge conditions in comparison to state-of-the-art kHz HHG sources. An evaluation of the photoelectron statistics of the setup by observing the temporal evolution of the relative standard deviation σ of the photoelectron spectrum proves the aptitude of our setup for high-precision, long-term PES experiments, with a statistical behaviour for up to 3×109 shots (see Fig. 1b). By measuring photoelectron spectra at different XUV flux, we show that no space charge within the instrumental resolution of 0.3 eV can be observed in a 10-μm-diameter focus spot. Our experiments reveal the XUV-IR-delay dependence of sidebands in the photoelectron spectrum generated by laser-assisted photoemission. This represents the first measurement with attosecond precision at MHz repetition rate.
关键词： High Harmonic Generation,Extreme-Ultraviolet,Ultrafast,Photoemission Spectroscopy,MHz repetition rates
更新于2025-09-16 10:30:52
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Above-threshold ionization driven by few-cycle spatially bounded inhomogeneous laser ?elds
摘要： In this work we study the main features of the photoelectrons generated when noble gas atoms are driven by spatially bounded inhomogeneous strong laser fields. These spatial inhomogeneous oscillating fields, employed to ionize and accelerate the electrons, result from the interaction between a pulsed low intensity laser and bow-tie shaped gold nanostructures. Under this excitation scheme, energy-resolved above-threshold ionization (ATI) photoelectron spectra have been simulated by solving the one-dimensional (1D) time-dependent Schr?dinger equation (TDSE) within the single active electron (SAE) approximation. These quantum mechanical results are supported by their classical counterparts, obtained by the numerical integration of the Newton-Lorentz equation. By using near infrared wavelengths (0.8 ? 3 μm) sources, our results show that very high energetic electrons (with kinetic energies in the keV domain) can be generated, far exceeding the limits obtained by using conventional, spatially homogeneous, fields. This new characteristic can be supported considering the non-recombining electrons trajectories, already reported by Neyra and coworkers (Neyra E, et al. 2018 J. Opt. 20 034002). In order to build a real representation of the spatial dependence of the plasmonic-enhanced field in an analytic function, we fit the generated 'actual' field using two Gaussian functions. We have further analyzed and explored this plasmonic-modified ATI phenomenon in a model argon atom by using several driven wavelengths at intensities in the order of 1014 W/cm2. Throughout our contribution we carefully scrutinize the differences between the ATI obtained using spatially homogeneous and inhomogeneous laser fields. We present the various physical origins, or correspondingly distinct physical mechanisms, for the ATI generation driven by spatially bounded inhomogeneous fields.
关键词： ultrafast optics,Above-threshold ionization,plasmonic fields
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) - Buildup of Noise-Like Pulses in Ultrafast Fiber Lasers
摘要： Noise-like pulses (NLP) - the emission of sub-nanosecond incoherent pulses in ultrafast lasers - are a topic of widespread attention, owing to their fundamental and applied interest [1]. Their existence seems paradoxical, combining the high temporal localization of circulating pulses akin to mode-locking, with a fundamental instability that entails large fluctuations [2]. NLPs can be considered as incoherent dissipative solitons [3]. It is therefore of considerable interest to investigate the self-emergence of these pulses in the laser. We undertake this study experimentally using the time-stretch dispersive Fourier transform (DFT), recording the pulse spectral and temporal information in real time over successive cavity roundtrips [4]. The buildup dynamics of noise-like pulses in both anomalous and normal-dispersion fiber lasers are compared, revealing markedly different stages and timescales in the evolution process.
关键词： anomalous dispersion,normal dispersion,Noise-like pulses,ultrafast fiber lasers,dispersive Fourier transform
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) - Phase-Locked Programmable Femtosecond Pulse Bursts from a Regenerative Amplifier
摘要： We demonstrate phase-controlled pulse-burst amplification based on differential pathlength stabilization between the master oscillator and the amplifier cavities. This technique boosts the safe level of extractable burst energy and suppresses fluctuations in various burst-mode applications. OCIS codes: (190.4410) Nonlinear optics, parametric processes; (320.5540) Pulse shaping; (320.7160) Ultrafast technology Generation of amplified bursts of femtosecond pulses with tunable and extremely high, reaching into the THz regime, intra-burst frequencies is in high demand for various ultrafast laser applications such as burst-mode femtosecond ablation for materials processing [1], multipulse laser-induced breakdown spectrometry, several types of nonlinear and/or time-resolved spectroscopies and molecular quantum-information technologies [2]. In many cases, the desired inter-pulse spacing within a burst must range from 10 fs to several ps and is limited on the short side by the duration of an individual compressed fs pulse that dictates the minimum pulse separation without significant temporal overlap. In this contribution, we explore the opposite limit of the Vernier technique[3] and generate THz burst frequencies, which requires us to solve the problem of a nearly complete temporal overlap of the chirped pulse replicas enclosed in the RA and present a method for interferometrically stabilizing the relative pathlength difference between ?(cid:2)?(cid:4) and control of the carrier-envelope phases, CEP, of the pulses forming the (Fig.1a). We note, that the standard method practiced in femtosecond comb metrology and synchronously pumped OPOs are not appropriate in our case because the roundtrip time of one of the cavities must be flexibly varied to ensure continuous tuning of (cid:5)(cid:6)(cid:7)(cid:8)(cid:9)(cid:10). Therefore, our approach relies on direct ?(cid:2) stabilization with a readout of a spectral interference fringe produced by overlapping an outgoing MO pilot pulse that has completed a roundtrip through the RA cavity with the next incoming MO pulse at the full MO repetition rate, (cid:5)(cid:11)(cid:12)(cid:13) 76 MHz. Active RA cavity length stabilization is achieved via a PZT on one of the fold mirrors. The CEP scrambling, needed to suppress the formation of spectral modes, is achieved by programming the RF signal in the AOM which permits simultaneous and independent phase and amplitude shaping of each successive MO pulse. Fig.1b proves that in this way it is feasible to control the mode formation in the amplified burst spectrum without affecting the temporal envelope of the burst. Without the CEP scrambling, the energy performance of the RA would be very significantly restricted because the optical damage threshold is lowered as a result of inter-pulse interference[3]. Fig 1c shows the resulting interference recorded in the reference arm at 8 seconds the control electronics is switched off and the cavity is left floating.
关键词： Nonlinear optics,Pulse shaping,parametric processes,Ultrafast technology
更新于2025-09-16 10:30:52
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[Laser Institute of America ICALEO? 2016: 35th International Congress on Applications of Lasers & Electro-Optics - San Diego, California, USA (October 16–20, 2016)] International Congress on Applications of Lasers & Electro-Optics - Ultrafast laser trepanning process and modeling
摘要： We present an engineering model of ultrafast laser ablation with normal or non-normal (oblique) laser beams. It can be applied to trepanning drilling but also to zero-taper cutting. Specific experiments on line ablation are presented to understand how oblique beams can control the walls conicity. Industrial strategies for processing with high throughput and high quality are considered.
关键词： ultrafast laser,industrial processing,oblique beams,ablation,zero-taper cutting,trepanning drilling
更新于2025-09-16 10:30:52
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Femtosecond lasers for high-precision orthopedic surgery
摘要： Laser micromachining with ultrashort pulses has shown great promise for clean, safe surgical treatment of bone tissue. However, comparisons of performance and development of “best practice” have been hampered by the difficulty of comparing results across a wide variety of experimental approaches and under surgically irrelevant conditions (e.g., dried, dead bone). Using a femtosecond (fs) pulsed laser system (τ = 140 fs, repetition rate = 1 kHz, λ = 800 nm), a comprehensive study of femtosecond laser microsurgery using the standard metrics of laser micromachining (ablation threshold, incubation effects, ablation rates, effect of focal point depth within the material and heat affected zone (HAZ)) was conducted on live, freshly harvested bovine and ovine cortical bone. Three important points of optimism for future implementation in the surgical theatre were identified: (1) the removal of material is relatively insensitive to the focal point depth within the material, removing the need for extreme depth precision for excellent performance; (2) femtosecond laser ablation of fresh bone demonstrates very little incubation effect, such that multiple passes of the laser over the same region of bone removes the same amount of material; and (3) the complete absence of collateral damage, heat- or shock-induced, on both the macro- and microscopic scales can be achieved readily, within a broad parameter range. Taken together, these results indicate a handheld or robotic deployed fiber laser platform for femtosecond laser microsurgery is a very viable prospect.
关键词： Laser ablation,Ultrafast laser micromachining,Femtosecond microsurgery,Laser micromachining,Orthopedic surgery
更新于2025-09-16 10:30:52
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NiPS <sub/>3</sub> nanosheets for passive pulse generation in an Er-doped fiber laser
摘要： With the rapidly increasing demands of industrial material processing, biomedical sensing, light detection, and high-speed communication, various novel two-dimensional (2D) materials have been synthesized and employed in ultrafast fiber laser generation due to their advantages of easy processing characteristics, desirable structures and excellent nonlinear optical properties. However, finding an efficient 2D material-based saturable absorber (SA) with the capacity of both high stability and excellent working property performance remains a challenge. Herein, high-quality NiPS3 crystals, from the metal phosphorus trichalcogenide (MPT3) family, were synthesized by a modified chemical vapor transport (CVT) method and a few-layer NiPS3 nanosheet SA was easily obtained using a direct liquid-phase exfoliation method. Different from other 2D materials, ultrathin NiPS3 nanosheets display a good stability. Moreover, a passively Q-switched operation and dual-wavelength mode-locked pulse output were proposed based on a NiPS3-SA erbium-doped fiber (EDF) laser. In the passively Q-switched operation, the maximum peak power was 6.40 mW with a maximum pulse energy of 29.66 nJ. It is also worth noting that dual-wavelength pulse output was achieved in passively mode-locked pulse generation. These results not only supply other choices of SAs for pulse generation, but also provide guidance to extend other possible applications of the MPT3 family for nonlinear optics.
关键词： mode-locked,Q-switched,NiPS3 nanosheets,ultrafast fiber laser,saturable absorber
更新于2025-09-16 10:30:52