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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) - Gain-Managed Nonlinear Fiber Amplifier
摘要： We demonstrate a novel pulse evolution in a fiber amplifier. We show that this pulse evolution is driven by a nonlinear attractor and paves the way toward simple, compact fiber systems producing high-energy, ~30-fs pulses.
关键词： Lasers, fiber,Nonlinear optics, fibers,Ultrafast lasers
更新于2025-09-11 14:15:04
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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) - Diamond Functionalization by Ultrafast Laser Pulses
摘要： The extreme material properties of diamond make it an attractive candidate for many technological applications. However, these same material properties often prove disruptive to the machining of diamond into functional devices. Ultrashort laser pulses focused inside diamond offer a potential new route for the functionalisation of diamond, offering a range of fabrication modalities on a single platform. Focusing beneath the surface of diamond, there is sufficient intensity from ultrashort laser pulses for non-linear absorption of light, which can lead to modification of the diamond lattice. The non-linearity of the process confines the modification to the focal volume of the laser, without effecting the diamond surface or surrounding regions. At high pulse energies (above ~100nJ), the laser deposits sufficient energy to break down the diamond lattice and induce a graphitic phase. Tracing the diamond through the laser focus allows the creation of conductive graphitic wires embedded inside the diamond in 3D. The processing becomes deterministic and the wire conductivity increases when the fabrication is carried out at high numerical apertures (NA = 1.4) [1]. The large refractive index mismatch at the diamond surface generates a depth dependent spherical aberration which should be corrected using adaptive optics. The laser written electrical wires can be used to fabricate radiation sensors, as shown in Fig. 1(a), which benefit from the radiation hardness of diamond. The advances in laser fabrication allow the realisation of new detector geometries. The graphitic inclusions fabricated by ultrashort pulse lasers beneath the surface of diamond exert stress on the surrounding diamond, which in turn modifies the optical properties of the crystal. By designing stress fields, it is possible to fabricate optical waveguides [2] and waveguide Bragg gratings [3] inside the diamond. In a different fabrication regime, it is also possible functionalise the diamond using ultrashort pulses without causing breakdown of the diamond lattice. We have shown that with a single ultrashort pulse it is possible to generate an ensemble of vacancies at the laser focus inside the diamond. A thermal anneal process heals any damage to the lattice and is successful in forming highly coherent isolated single nitrogen vacancy (NV) colour centres [4, 5]. We have recently demonstrated improvements to the method using a laser based localised anneal with fluorescence feedback to write arrays of NV centres with near unity yield and in-plane positioning accuracy of 40nm [6].
关键词： functionalisation,diamond,graphitic wires,ultrafast laser pulses,NV centres,optical waveguides
更新于2025-09-11 14:15:04
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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) - Optically Driven Attosecond Electron Dynamics in III-V Semiconductors
摘要： A fundamental understanding of ultrafast electron dynamics in solids induced by light is of great interest for future high-speed electro-optical devices operating in the petahertz frequency regime. In the last years, a number of publications demonstrated the possibility to resolve and control carrier dynamics in semiconductors and dielectrics on the few- to sub-femtosecond time scale using attosecond transient absorption spectroscopy (ATAS). These experiments were performed with a non-resonant pump pulse, i.e. pump photon energies smaller than the corresponding band gap. Here in contrast, we resolve for the first time the attosecond carrier dynamics induced by a resonant intense laser pulse. We study the attosecond electronic response in gallium arsenide (GaAs), a technologically important narrow band gap semiconductor.
关键词： gallium arsenide,III-V semiconductors,attosecond transient absorption spectroscopy,ultrafast electron dynamics,attosecond electron dynamics
更新于2025-09-11 14:15:04
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Generation of few-cycle laser pulses with high temporal contrast via nonlinear elliptical polarisation rotation in a hollow fibre compressor
摘要： We report on the simultaneous temporal filtering and compression of 30 fs laser pulses down to 5 fs duration via nonlinear elliptical polarization rotation (NER) in a stretched flexible hollow fibre compressor. Both the achieved 2-cycle pulse duration and the internal conversion efficiency of ～47% are solely limited by the applied fibre geometry. Our investigations show that precise control of the NER process could help significantly improve the temporal fidelity of high-energy hollow fibre compression schemes.
关键词： post-compression,ultrafast lasers,temporal contrast
更新于2025-09-11 14:15:04
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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) - Intra-Cavity Mode-Selective Coupler Assisted Ultrafast Cylindrical Vector Fiber Laser
摘要： Cylindrical vector beam (CVB) fiber lasers have attracted great attentions due to their promising applications in optical communications, super-resolution imaging and optical trapping. Recently, it has been proved that mode-selective coupler (MSC) is an efficient method for generating CVBs in all-fiber lasers [1-3]. However, to date, the reported MSC-assisted CVB lasers have a common feature that the fundamental transverse mode (LP01) oscillates in the laser cavity whereas the high-order modes are outside the laser cavity. To some extent, such cylindrical vector lasers belong to the external mode conversion, rather than the direct generation of high-order modes inside the laser cavity. In this contribution, we present an intra-cavity MSC assisted CVB fiber laser in a compact linear-cavity mode-locked by using a semiconductor saturable absorber mirror (SESAM). The laser architecture is shown in Fig. 1(a), which consists of a 5 m Er-doped fiber, a 980/1550 wavelength-division multiplexer (WDM) pumped by a 980 nm laser, a polarization controller (PC), a 90% high coupling ratio MSC with an insertion loss of 0.3 dB. A fiber end-facet mirror is sandwiched between the two fiber ferrules and a SESAM mode locker has a modulation depth of 18%. The rest of cavity consists of ~14.3 m standard single-mode fiber (SMF) and ~0.6 m few mode fiber (FMF). Self-started mode-locking occurs when the pump power reaches ~35 mW. Thanks to the high coupling efficiency of intra-cavity mode converter, LP01 mode in the SMF is sufficiently coupled to LP11 mode in the FMF when it passes through the MSC. The reflected LP11 mode from the mirror can be partially coupled back to the SMF with a low loss, resulting in the laser oscillation. In this case, the laser operates between MSC and the mirror in the LP11 mode, which outputs from the FMF, meanwhile the LP01 mode oscillates in the remaining section of the linear-cavity. Eventually, the laser can allow the direct generation of LP11 mode from the laser cavity. Typical laser output characteristics such as broadband spectra, pulse train and output power are shown in Fig. 1(b)-(e). The laser operates at the wavelength of 1562 nm with a 3-dB bandwidth of ~4.4 nm and a repetition rate of 5.2 MHz. Radially polarized and azimuthally polarized ultrafast CVBs are obtained by adjusting the PC, and corresponding donut beam profiles are demonstrated by checking the rotating intensity distribution through the linear polarizer, as presented in Fig. 1(f).
关键词： Cylindrical vector beam,mode-selective coupler,ultrafast,fiber laser
更新于2025-09-11 14:15:04
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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 - The role of pulse to pulse interactions during usp-laser ablation with high average power and repetition rates
摘要： Ultrafast lasers are a versatile tool for micro processing for a wide range of materials. One common field of application is e.g. the surface structuring for mold and embossing tools. While the extremely short pulse durations < 10 ps and interaction times enable highly precise processing quality, the productivity is one major issue and much too small for many industrial applications. To improve the productivity and throughput, increasing the applied average power is a key parameter. Therefore, ultrafast lasers with high average power have the potential to scale up the productivity and reduce the processing times significantly. We present investigations on the processing of metals with a multi-100 W ultrafast laser system with pulse repetition rates of up to 20 MHz. For such power levels and high repetition rates effects like heat accumulation and shielding by pulse-plume interactions occur and have to be taken into account. We describe the relevance and impact of process parameters like spatial pulse separation, repetition rate and pulse duration on the productivity of the ablation process. A theoretical model is presented to distinguish between the influences of the aforementioned effects on the experimental results. Moreover, the fabrication of surface structures utilizing multi-100 W average power is presented.
关键词： ultrafast lasers,repetition rates,heat accumulation,pulse-plume interactions,high average power,micro processing
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Miramar Beach, FL, USA (2019.8.19-2019.8.21)] 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Mid-IR Ultrafast Laser Inscribed Waveguides and Devices
摘要： Ultrafast laser inscription (ULI) is a highly versatile technique for creating index modifications in glasses and crystalline materials. The process of ULI relies on ultrashort laser pulses focused inside of a material. The high intensity of the pulsed beam induces nonlinear absorption processes, which transfers the pulse energy to the material lattice. With careful experimental control of the laser parameters, a permanent change in the refractive can be obtained in the bulk material. The permanent refractive index change obtained by ULI can be used to create waveguides and devices in active and passive materials. In this work, we present recent advances on creation of guided wave devices in Mid-IR compatable materials such as Fe:ZnSe, Cr:ZnSe, Ho:YAG, LiNbO3, and CdSiP2.
关键词： Ultrafast Laser Inscription,Solid-state lasers,Infrared Lasers
更新于2025-09-11 14:15:04
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Complex-conjugate Pole-residue Pair-Based FDTD Method for Assessing Ultrafast Transient Plasmonic Near Field
摘要： The study of the optical properties of plasmonic nanostructures in the stationary regime has greatly benefited from the development of numerical methods, among which Finite Difference Time Domain (FDTD) is popular. In contrast, the use of these numerical tools for assessing the transient plasmonic optical response triggered by ultrashort laser pulses is hampered by the difficulty to address small variations of the material optical properties with reasonable computational time. Yet, many of the developments based on this ultrashort response rely on the dynamics of the near-field topography around the nanostructures. In this article, we present a way to bridge this gap with the complex-conjugate pole-residue pair (CCPRP) approach. A CCPRP-based FDTD simulator has been developed. First, a simple methodology to check the end-to-end accuracy of the FDTD simulation is provided. Then, in conjunction with a three-temperature model, the approach enables us to calculate the ultrafast transient near field inside and around a gold nanoparticle (AuNP) upon absorption of a subpicosecond laser pulse. The transient variation of the field intensity inside and around the AuNP is compared with the one determined by the Mie theory. The dependence of the transient field intensity on the distance away from the nanoparticle surface and on the delay time after laser pulse absorption is finally analyzed.
关键词： Ultrafast,Complex-conjugate pole-residue pairs,Nanoparticles,Plasmonics,Near-field enhancement,FDTD
更新于2025-09-11 14:15:04
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Femtosecond Soliton Erbium-doped Fiber Laser with a Symmetrical GIMF-SIMF-GIMF Saturable Absorber
摘要： A femtosecond soliton erbium-doped fiber ring laser with the symmetrical saturable absorber (SA) of graded index multimode fiber-step index multimode fiber-graded index multimode fiber (GIMF-SIMF-GIMF) is proposed and proved. Based on the nonlinear multimode interference (NL-MMI) effect of SA, the fiber laser achieved femtosecond soliton mode-locking operation and repetition rate tuning. The duration of soliton was 364 fs at 1562.5 nm and repetition rate was tunable from 10.29 MHz to 763.36 MHz. In the structure of SA, a short step index multimode fiber (SIMF) was inserted between two graded index multimode fibers (GIMFs) to generate more high-order modes，adjust the self-focusing length, and improve operation stability of mode-locked fiber laser. The SA also has the advantages of immunity to the external environment variation, high damage threshold and inoxidizability, which make the laser operate stably for a long time.
关键词： Femtosecond soliton,ultrafast fiber lasers.,mode-locked fiber lasers,nonlinear multimode interference
更新于2025-09-11 14:15:04
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Microwelding of glass to silicon by green ultrafast laser pulses
摘要： In the present work, a direct bond between glass and silicon with optical contact was formed by 515 nm picosecond laser controlled by the galvanometer scanning system. A crack-free welding effect without edge breakage and residues was obtained with breaking strength as high as 122 MPa. New crystalline phase (SiO2) was produced and silicon and oxygen have a spatial distribution gradient in the welding area analyzed by XRD and EDS, respectively, revealing that mixing and inter-diffusion of substances have occurred during laser irradiation. The transmission of near infrared light in the welding area is significantly increased compared with the non-welding area analyzed by inverted microscope. A confocal laser scanning microscope was used to observe the morphology and width of welds, which variation trend of axial focal positions is consistent with the teardrop structure produced by nonlinear absorption effect. Scanning speeds and laser repetition frequencies also affect the width and morphology of the weld.
关键词： Silicon,Glass,Microwelding,Ultrafast laser
更新于2025-09-11 14:15:04