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- 摘要
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Lasers for Novel Accelerators
摘要： Novel accelerator schemes are rapidly emerging in the wake of laser-plasma acceleration research and involve advanced high-power laser drivers for their operation. Significant progress has been made in laser performance during the past decade, including repetition rate, average and peak power, and footprint, making these systems attractive for many applications, including novel accelerators. Here we discuss laser driver requirements for the proposed novel accelerator schemes, examine emerging technologies and introduce a viable laser driver concept for a first generation of plasma accelerators.
关键词： novel accelerators,lasers,laser-plasma acceleration,high-power laser drivers
更新于2025-09-12 10:27:22
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High Power Quantum Cascade Laser at λ 5.1 <i>μ</i> m Based on Low Strain Compensation Design
摘要： We demonstrate the development of a high performance quantum cascade laser at (cid:2) ～ 5(cid:3)1 (cid:4)m with low strain-balanced structure using a double-phonon resonant design approach. The wafer was grown by solid source molecular beam epitaxy and fabricated with buried heterostructure waveguides. A high output power up to 1.5 W is obtained at 288 K with a high wall plug ef?ciency of 8.5% for devices with stripe dimension of 5 mm × 10 (cid:4)m. The characteristic temperatures, T 1, are 114 K and 198 K respectively.
关键词： High Power Laser,Strain-Compensation,Quantum Cascade Laser
更新于2025-09-12 10:27:22
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Avoidance of end crater imperfections at high-power laser beam welding of closed circumferential welds
摘要： The present work deals with the development of a strategy for the prevention of end crater defects in high-power laser welding of thick-walled circumferential welds. A series of experiments were performed to understand the influence of the welding parameters on the formation of end crater defects such as pores, cracks, root excess weld metal and shrinkage cavities in the overlap area. An abrupt switch-off of the laser power while closing the circumferential weld leads to a formation of a hole which passes through the whole welded material thickness. A laser power ramp-down causes solidification cracks which are initiated on the transition from full-penetration mode to partial penetration. Defocusing the laser beam led to promising results in terms of avoiding end crater defects. Cracks and pores in the overlap area could be effectively avoided by using defocusing techniques. A strategy for avoiding of end crater imperfections was tested on flat specimens of steel grade S355 J2 with a wall thickness of between 8 and 10 mm and then transferred on the 10 mm thick pipe sections made of high-strength pipeline steel API5L-X100Q.
关键词： Thick-walled pipes,End crater,Circumferential weld,High-power laser beam,Laser beam welding
更新于2025-09-12 10:27:22
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Numerical simulations to study turbulent magnetic field amplification by nonlinear interaction of high-power laser and kinetic Alfvén waves in laboratory and astrophysical plasmas
摘要： The model contouring the dynamics of transient nonlinear interaction between the high-frequency extraordinary-elliptically polarized laser (HFXPL) and low-frequency kinetic Alfvén wave (LFKAW) dynamics in the magnetized plasma is the focal point of the present investigation. The quasistatic ponderomotive force driven by the HFXPL pump induces density cavitation and humps in the low-frequency kinetic Alfvén wave. In order to study the intricate localized structures of HFXPL pump waves that evolve with time, the requisite dimensionless equations of the coupled system (HFXPL and LFKAW) are evaluated by using numerical methods in the nonlinear stage. The typical scale sizes of these structures in the early phase are ≈9 μm, and the typical time to grow is ≈10 ps. The ensemble-averaged magnetic power spectra are also presented, indicating energy cascade. The rendered investigations follow direct relevance to the experimental observations and are imperative in understanding turbulence in astrophysical scenarios.
关键词： kinetic Alfvén waves,high-power laser,astrophysical plasmas,laboratory plasmas,nonlinear interaction,turbulent magnetic field amplification
更新于2025-09-12 10:27:22
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Weld pool shape observation in high power laser beam welding
摘要： The geometry of the melt pool in laser beam welding plays a major role to understand the dynamics of the melt and its solidification behavior. In this study, a butt configuration of 15 mm thick structural steel and transparent quartz glass was used to observe the weld pool geometry by means of high-speed camera and an infrared camera recording. The observations show that the dimensions of the weld pool vary depending on the depth. The areas close to the weld pool surface take a teardrop-shape. A bulge-region and its temporal evolution were observed approximately in the middle of the depth of the weld pool. Additionally, a 3D transient thermal-fluid numerical simulation was performed to obtain the weld pool shape and to understand the formation mechanism of the observed bulging effect. The model takes into account the local temperature field, the effects of phase transition, thermo-capillary convection, natural convection and temperature-dependent material properties up to evaporation temperature. The numerical results showed good accordance and were furthermore used to improve the understanding of the experimentally observed bulging effect.
关键词： high power laser beam welding,transient weld pool shape,bulging,numerical process simulation
更新于2025-09-12 10:27:22
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Surface treatments of forged steel AISI6F3 by using high power CO <sub/>2</sub> laser
摘要： The hardness of forging dies is highly affected by the hot forming processes; especially by the long exposure to a wide thermal range, which leads to a decline in the level of hardness due to the tempering of the microstructure, thus failure occurs and the die breaks. The microstructure and hardness have been studied to demonstrate the relationship between them and their direct effect on the regions generated by the laser treatment of high capacity. The selected samples were chosen within a combination of laser variables to reach the appropriate structure that achieves the best hardness and indeed the highest hardness value (965 Hv) with laser processing parameters included the power 3000 W, beam diameter 1mm and scanning speed 25 mm/s with its characteristic microstructure as well as its high cooling rate.
关键词： High power laser,Forged steel,Hardness,Microstructure
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE Photonics Conference (IPC) - San Antonio, TX, USA (2019.9.29-2019.10.3)] 2019 IEEE Photonics Conference (IPC) - High-Power Ultrafast Industrial Thin-Disk Lasers
摘要： Ultrafast amplifiers using industrial thin-disk technology from TRUMPF deliver record pulse energies of 200 mJ at 5 kHz. In addition, multipass amplifiers to increase the average power and pulse energy and concepts for nonlinear compression to reach pulse durations below 50 fs will be discussed.
关键词： diode-pumped,ultrafast,high-energy,Thin-disk laser,amplification,high-power,laser amplifier,X-ray
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) - Pulsed Yb-Doped Phospho-Silicate Fiber MOPA Source with 25kW Peak Power and Excellent Beam Quality
摘要： With ytterbium doped fiber (YDF) lasers and amplifiers have reached continuous wave output power of multi-kW with direct diode pumping [1] and 10kW with tandem pumping [2] in a good beam quality, today fiber lasers are becoming the laser choice for many industrial applications and processes, defense, and scientific research. One of the challenges of high average power fiber laser is to maintain a long-term stability of the output power. In particular, photodarkening (PD) is seen as a power loss in YDF gain medium that can significantly influence the operation lifetime of the device. Moreover, it was observed that the PD is related to the transverse mode instability (TMI) that can limit the output power of the laser [3]. In silica host, co-dopant phosphorous (P) is more effective than aluminium (Al) to suppress the PD effect in YDF. In addition, Yb-doped phosphosilicate (Yb-PS) fiber is found suitable for high power laser operation below 1020nm [4]. Such lasers are used as pumps in tandem pumping to reduce the heat load associated with the quantum defects in YDF lasers operating at 10kW level [4]. However, Yb-PS fiber are generally considered difficult to fabricate due to evaporation of P2O5 during the preform fabrication process, resulting in a central dip in the core refractive index profile that has detrimental effect on the output beam quality of fiber lasers. Other disadvantage of P co-doping is its smaller Yb - absorption and emission cross-sections compared to Al counterpart. To compensate for the cross-sections, higher concentrations of Yb and P (to prevent Yb ions from clustering) are needed in fiber. This contributes to a high core NA and poses a challenge to fabricate a large mode area Yb-PS fiber. Here we report an efficient Yb-PS high power laser fiber fabricated using an optimized MCVD (modified chemical vapor deposition) and all-vapor-phase chelate precursor doping technique. Double-clad fiber with a 150μm quasi-octagonal inner cladding and a 12μm core diameter was drawn with a low index polymer outer cladding. The core NA was 0.1, Fig.1 (a). The small signal absorption at the pump wavelength of ~976nm was measured as 2.5 dB/m. Initially the fiber was tested in a 4%-4% laser cavity. An output power of >100W (limited by the available pump power) and the slope efficiency of >85% were obtained. The laser emission was centered at 1066nm. We then tested the same fiber in a pico-second MOPA configuration. Fig. 1(b) shows the experimental schematic. A 4m long Yb-PS fiber was used in the final stage of the MOPA. A gain-switched diode operating at ~1035nm with 180ps pulse width and 2.95MHz repetition rate was used as a seed laser. Fig. 1(c) shows the average signal output power with respect to the absorbed pump power in the final stage of the amplifier. The output power reached 13.3W and the slope efficiency was 74%. The corresponding pulse energy and peak power was 4.5μJ and 25kW respectively. The measured beam quality (M2) was ~ 1.13, as shown in inset of Fig. 1(c). The spectra of the seed laser and at the maximum signal output power are shown in Fig. 1(d). The 3dB spectral bandwidth at the maximum output power was measured as 0.29nm compared to 0.03nm of the seed laser. The magnitude of the stimulated Raman scattering (SRS) appeared at a wavelength of ~1080nm was 30dB lower than the output signal – see Fig. 1(d). In conclusion, we have demonstrated that an all-vapor-phase chelate doping technique holds great potential to fabricate LMA Yb-doped phosphosilicate fibers with diffraction limited beam for high power lasers.
关键词： high power laser,Yb-doped phosphosilicate fiber,photodarkening,all-vapor-phase chelate precursor doping,transverse mode instability,MCVD
更新于2025-09-11 14:15:04
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AIP Conference Proceedings [AIP Publishing LLC EXOTIC NUCLEI AND NUCLEAR/PARTICLE ASTROPHYSICS (V). FROM NUCLEI TO STARS: Carpathian Summer School of Physics 2014 - Sinaia, Romania (13–26 July 2014)] - Perspectives for neutron and gamma spectroscopy in high power laser driven experiments at ELI-NP
摘要： The measurement of energy spectra of neutrons and gamma rays emitted by nuclei, together with charge particles spectroscopy, are the main tools for understanding nuclear phenomena occurring also in high power laser driven experiments. However, the large number of particles emitted in a very short time, in particular the strong X-rays flash produced in laser-target interaction, impose adaptation of technique currently used in nuclear physics experiment at accelerator based facilities. These aspects are discussed (Section 1) in the context of proposed studies at high power laser system of ELI-NP. Preliminary results from two experiments performed at Titan (LLNL) and ELFIE (LULI) facilities using plastic scintillators for neutron detection (Section 2) and LaBr3(Ce) scintillators for gamma detection (Section 3) are presented demonstrating the capabilities and the limitations of the employed methods. Possible improvements of these spectroscopic methods and their proposed implementation at ELI-NP will be discussed as well in the last section.
关键词： gamma spectroscopy,neutron spectroscopy,nuclear physics,ELI-NP,high power laser
更新于2025-09-11 14:15:04
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High power all-fiberized and narrow-bandwidth MOPA system by tandem pumping strategy for thermally induced mode instability suppression
摘要： An all-?berized and narrow-bandwidth master oscillator power ampli?cation (MOPA) system with record output power of 4 kW level and slope ef?ciency of 78% is demonstrated. Tandem pumping strategy is tentatively introduced into the narrow-bandwidth MOPA system for thermally induced mode instability (TMI) suppression. The stimulated Brillouin scattering (SBS) effect is balanced by simply using one-stage phase modulation technique. With different phase modulation signals, SBS limited output powers of 336 W, 1.2 kW and 3.94 kW are respectively achieved with spectral bandwidths accounting for 90% power of ～0.025, 0.17 and ～0.89 nm. Compared with our previous 976 nm pumping system, TMI threshold is overall boosted to be >5 times in which tandem pumping increases the TMI threshold of >3 times. The beam quality (M 2 factor) of the output laser is well within 1.5 below the TMI threshold while it is ultimately saturated to be 1.86 with the in?uence of TMI at maximal output power. Except for SBS and TMI, stimulated Raman scattering (SRS) effect will be another challenge for further power scaling. In such a high power MOPA system, multi-detrimental effects (SBS, SRS and TMI) will coexist and may be mutual-coupled, which could provide a well platform for further comprehensively investigating and optimizing the high power, narrow-bandwidth ?ber ampli?ers.
关键词： optimization,design,laser ampli?ers,narrow linewidth,high power laser,laser systems,modeling,advanced laser technology and applications,?ber laser and applications
更新于2025-09-10 09:29:36