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Annealing effect on laser-induced magnetization dynamics in Co/Ni-based synthetic antiferromagnets with perpendicular magnetic anisotropy
摘要： We report a comprehensive study of annealing treatment modulation on the laser-induced ultrafast magnetic behaviors in antiferromagnetically exchange-coupled [Ni/Co]4/Ru/[Co/Ni]3 multilayers with perpendicular magnetic anisotropy (PMA). Magnetic hysteresis loops indicate that the uniaxial PMA ?eld Hkeff decreases monotonously with the increase in annealing temperature Ta, but the variation of interlayer coupling ?eld Hex is rather complicated. Time-resolved magnetic-optical Kerr effect (MOKE) measurements demonstrate that the laser-excited demagnetization and precession process relies signi?cantly on Ta. Upon laser impulsion, the MOKE signal immediately shows a nonchanging transient increase and decrease with H increasing for low Ta, but only the ultrafast decreasing behavior for high Ta. From the subsequent dynamic precession spectra, the optical and acoustic precession modes are identi?ed. By ?tting the ?eld-dependent frequency curves via the deduced dispersion relations, both Hkeff and Hex are determined and their variation trends agree well with the results from the static magnetic measurement. Moreover, it is found that the critical ?eld where the ultrafast signal decrease occurs is dependent on the co-effect of Hkeff and Hex, whereas the maximum ?eld at which the optical mode precession disappears shares the same trend as Hex. The magnetic damping of acoustic mode is seen to increase with Ta due to the increased inhomogeneities. Our ?ndings provide a deep understanding of the magnetic properties in synthetic antiferromagnetic multilayers with high annealing temperatures, which will be helpful for designing advanced spintronic devices.
关键词： time-resolved magnetic-optical Kerr effect,laser-induced ultrafast magnetic behaviors,annealing treatment,synthetic antiferromagnets,perpendicular magnetic anisotropy
更新于2025-09-16 10:30:52
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High Energy and Short Pulse Lasers || Phase Manipulation of Ultrashort Soft X-Ray Pulses by Reflective Gratings
摘要： In this chapter, we discuss the use of reflective diffraction gratings to manipulate the phase of ultrashort pulses in the extreme ultraviolet (XUV) and soft X-ray spectral regions. Gratings may be used to condition the spectral phase of ultrashort pulses, e.g., to compensate for the pulse chirp and compress the pulse, similarly to what is routinely realized for visible and infrared pulses. The chirped pulse amplification technique has been already proposed for soft X-ray free-electron laser radiation; however, it requires the use of a compressor to compensate for the pulse chirp and get closer to the Fourier limit. There are fundamental differences when operating the gratings at wavelengths shorter than ≈40 nm on a broad band: (a) the gratings are operated at grazing incidence; therefore, the optical design has to be consequently tailored to this peculiar geometry; (b) the grating efficiency is definitely lower; therefore, the number of diffractions has to be limited to two. We discuss the different configurations that can be applied to the realization of a grating stretcher/compressor.
关键词： extreme ultraviolet,soft X-ray optics,ultrafast optics,diffraction gratings,chirped pulse amplification
更新于2025-09-16 10:30:52
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Advances in Ultrafast Optics || 1. Ultrafast ultrahigh-intensity laser pulses
摘要： Generation of high intensity laser pulses has been regarded as one of the most important research topics since the invention of lasers. High intensity lasers are normally constructed using the master oscillator power amplifier (MOPA) configuration to boost the energy of short laser pulses. This configuration has been used in various locations such as the Shenguang facilities in China and the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL) in the USA; the latter is currently the largest laser facility in the world. This type of giant laser facility is usually employed for high-cost and large-scale scientific projects involving complex technology and only a few countries can perform this type of laser research. Because of the low repetition rate and long pulse duration of the achieved laser pulses, these laser facilities are not suitable for large-scale applied research. Furthermore, the output laser intensity is limited. For example NIF, constructed in 2009, includes 192 ultraviolet (UV) beams with the total energy up to 1.8 megajoules (MJ, 106 J). However, the peak power is only approximately 500 terawatts (TW; 1012 W) [1] because the pulse duration is at the nanosecond (ns; 10?9 s) level; the separation time between two pulses is as long as a few hours. At the other end of the scale, several research institutes have developed tabletop laser systems within regular-scale labs through the amplification of ultrashort-pulse lasers at the femtosecond (fs; 10?15 s) level. These lasers have peak powers at the petawatt (PW; 1015 W) level [2–4], a repetition rate of 1 hertz (Hz) [5], and a focus intensity reaching 1022 W/cm2 [6]. As a result of the 1991 discovery of the Kerr-lens mode-locking (KLM) phenomenon by the Sibbett group in the UK [7], along with the development of chirped pulse amplification (CPA) technology by the US-based Mourou group in 1985 [8], and research on ultrashort pulses, ultrahigh-intensity lasers have been advancing at an unprecedented pace since the late 1980s. New scientific records associated with significant breakthroughs have been made on a continuous basis. Ultrashort-pulse laser research has developed in two explorative directions. One path of development targets extremely short pulse duration promoted by mode-locking technology. Currently, laser pulse duration can reach the few-cycle level; in addition, attosecond (as; 10?18 s) laser pulses can be achieved using new physical mechanisms [9–11]. The second research trend is the ongoing extension of the laser peak power limit. An increasing number of femtosecond ultrahigh-intensity laser facilities with peak powers at the terawatt or even petawatt level have been developed [2–5], serving as powerful tools for in-depth research on ultrafast, ultrahigh-intensity laser pulses. Ultrashort pulses and ultrahigh-intensity laser technology are not only extensively employed in the fields of micromanufacturing [12–14] and medicine [15, 16] but have also been successfully and prominently implemented in various research areas, such as the exploration of atomic and molecular motion patterns [17, 18], laboratory simulations in astrophysics [19], and precision spectroscopy [20]. These applications have facilitated the emergence of many new subfields and groundbreaking scientific achievements. One of the two most representative events was the award of the 1999 Nobel Prize in Chemistry to the American researcher, Prof. A. H. Zewail. This prize was awarded for work on chemical kinetics using femtosecond laser pulses. The second representative achievement was the joint sharing of one half of the 2005 Nobel Prize in Physics by Profs. J. L. Hall and T. W. H?nsch; this prize was awarded for their achievements regarding the femtosecond laser frequency comb technique. With state-of-the-art features and innovative applications, ultrashort pulses, ultrahigh-intensity lasers have become crucial tools in the field of optical physics. Therefore, this chapter will first briefly review the essential technology and associated progress in research.
关键词： ultrahigh-intensity lasers,femtosecond lasers,laser technology,Kerr-lens mode-locking,petawatt lasers,optical physics,chirped pulse amplification,ultrafast lasers
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - 100 MHz Reconfigurable Ultrafast Swept Source by Time Stretching of 100 nm Flat-top Spectrum
摘要： The repetition rate of swept source determines the acquisition rate of optical coherence tomography and interrogation rate of optical sensing systems. The axial resolution of optical coherence tomography is limited by the swept range of the swept source. In this paper, we report an ultrafast time stretching swept source with up to 100 MHz repetition rate and a 100 nm flattop spectrum. The repetition rate can be reconfigured by incorporating with an optical modulator.
关键词： Time stretching,Ultrafast swept source
更新于2025-09-16 10:30:52
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Editorial: Lasers in Accelerator Science and Secondary Emission Light Source Technology
摘要： Unifying laser and accelerator physics holds great promise for the development of future particle accelerators, light sources, and other scienti?c instruments due to increasingly synergistic advances at the cross section between these two ?elds. Their combined action has recently ushered in advanced accelerator facilities around the world that have enabled unique scienti?c and technological breakthroughs: from advanced electron and ion sources for high-energy physics to the ultrabright x-ray pulses to study ultrafast phenomena at elemental spatio-temporal scales [1–4]. The progress of ultra-intense femtosecond lasers, now attaining multi PetaWatt peak power, has recently enabled the demonstration of GeV electron beams in centimeter scale plasma accelerating section [5, 6], with the recent world record reaching 8 GeV in 20 cm [7]. As for ultrafast x-ray science, in their relatively short time since their advent, x-ray free electron lasers [8, 9] (FEL) have demonstrated the capacity to answer grand fundamental questions in a diverse set of areas in physics, chemistry, and biology, such as revealing vibration coherence in molecules [10], molecular bond formation, charge migration, and dissociation dynamics [11, 12], or ultrafast isomerization in biomolecules [13, 14], among many others. Further advances in facilities—such as augmented brightness, attosecond duration, or seeded emission—are poised to creating new scienti?c frontiers in atomic-scale correlated systems and ultrahigh resolution inner shell spectroscopies.
关键词： free electron laser (FEL),ultrafast optics,X-ray emission,non-linear optics,laser accelerated particles,secondary emission and photoemission
更新于2025-09-16 10:30:52
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Lyot Filter With Femtosecond Laser-Induced High Birefringence Single-Mode Fiber for Torsion, Transverse Load and Temperature Sensing
摘要： We propose and experimentally demonstrate an all-fiber Lyot filter with femtosecond laser-induced high birefringence single-mode fiber (SMF) for torsion, transverse load and temperature sensing. With the femtosecond-laser processing technique, the SMF with the birefringence of 2.81×10?4 is manufactured by directly writing a straight cladding stress track parallel with fiber core and employed to form an all-fiber Lyot filter for sensing application. The sensitivities of the all-fiber Lyot filter with respect to torsion, transverse load and temperature are found to be ?4265.669 nm/(rad/mm), ?321.004 nm/(N/mm), and 0.271 nm/?C, respectively. The experimental results are powerful proof of the excellent performance of the femtosecond laser-induced high birefringence SMF based all-fiber Lyot filter for sensing application, which not only adds significantly new and important results to the fields of optical sensing, but also develops the application fields of femtosecond-laser processing technique and all-fiber Lyot filter.
关键词： filters,polarization interference,Optical fiber sensors,ultrafast processes in fibers,fiber birefringence
更新于2025-09-16 10:30:52
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Femtosecond Laser-Induced Electron Emission from Nanodiamond-Coated Tungsten Needle Tips
摘要： We present femtosecond laser-induced electron emission from nanodiamond-coated tungsten tips. Based on the shortness of the femtosecond laser pulses, electrons can be photoexcited for wavelengths from the infrared (1932 nm) to the ultraviolet (235 nm) because multiphoton excitation becomes efficient over the entire spectral range. Depending on the laser wavelength, we find different dominant emission channels identified by the number of photons needed to emit electrons. Based on the band alignment between tungsten and nanodiamond, the relevant emission channels can be identified as specific transitions in diamond and its graphitic boundaries. It is the combination of the character of initial and final states (i.e., bulk or surface-near, direct or indirect excitation in the diamond band structure), the number of photons providing the excitation energy, and the peak intensity of the laser pulses that determines the dominant excitation channel for photoemission. A specific feature of the hydrogen-terminated nanodiamond coating is its negative electron affinity that significantly lowers the work function and enables efficient emission from the conduction band minimum into vacuum without an energy barrier. Emission is stable for bunch charges of up to 400 electrons per laser pulse. We infer a normalized emittance of <0.20 nm rad and a normalized peak brightness of >1.2 × 1012 A m?2 sr?1. The properties of these tips are encouraging for their use as laser-triggered electron sources in applications such as ultrafast electron microscopy as well as diffraction and novel photonics-based laser accelerators.
关键词： nanodiamond,ultrafast electron microscopy,tungsten tips,multiphoton excitation,electron emission,negative electron affinity,femtosecond laser
更新于2025-09-16 10:30:52
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CFBG Based Bidirectional Mode-locked Fiber Laser Emitting Conventional and Dissipative Solitons
摘要： We report on the multi-state soliton generation in a chirped fiber Bragg grating (CFBG) based bidirectional mode-locked fiber laser. In particular, a θ-shape associate cavity is designed to introduce reverse dispersion distributions in counter-propagation directions through the bidirectional reflection of the CFBG into the lasing oscillator. With a relatively compact cavity configuration, the clockwise (CW) and counterclockwise (CCW) directions are managed into large anomalous and normal dispersion regimes, respectively. Consequently, conventional solitons (CSs) and dissipative solitons (DSs) can be emitted from the counter-propagation directions. To the best of our knowledge, it is the first report of CS/DS generation in a CFBG based bidirectional fiber laser. This investigation can contribute to research community of multiplexed ultrafast fiber lasers.
关键词： Fiber lasers,ultrafast optics,bidirectional cavity,fiber grating,laser mode locking
更新于2025-09-16 10:30:52
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Numerical Investigation on the Influence of Water Vapor Ionization on the Dynamic and Energy Deposition of Femtosecond Ultraviolet Laser Filamentation in Air
摘要： The e?ects of water vapor ionization on the nonlinear propagation of femtosecond laser pulses with a 248 nm wavelength are numerically investigated in this paper. It is found that ionization of H2O molecules plays a signi?cant role in air ionization, which seriously a?ects the dynamic and energy deposition of ?lamentation. The propagation of femtosecond pulses in air with di?erent humidity levels are compared. The total number of electrons and total deposited pulse energy increase with the humidity increases. However, they tend to be saturated in high humidity conditions. Results presented here are conducive to characterizing the long-range propagation of ?laments under atmospheric conditions.
关键词： multiphoton absorption,atmospheric propagation,self-focusing,water vapor,ultrafast nonlinear optics
更新于2025-09-16 10:30:52
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Optimal output coupler grating reflectivity for Er/Yb fiber lasers
摘要： We measure the output power of an Er/Yb fiber laser with twelve different SMF-28 narrowband output couplers and demonstrate experimentally that the optimal reflectivity is ~1%. The fiber laser efficiency with the optimal output coupler is ~38% at ~1546 nm. In addition, we successfully inscribe a similar output coupler in situ during laser operation with 800 nm femtosecond pulses and the phase mask technique. An output power very close to the optimal was obtained with the in situ inscribed output coupler. With a flat cleaved broadband output coupler, the efficiency is ~42%, which is the highest reported efficiency of an Er/Yb fully integrated fiber laser.
关键词： Fiber lasers,Fiber Bragg gratings,Ultrafast optics
更新于2025-09-16 10:30:52