- 标题
- 摘要
- 关键词
- 实验方案
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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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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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[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) - Optimisation of Dispersion Flatness in Nanostructured Core Fibres
摘要： Nanostructured optical fibres allow to obtain an arbitrary profile of refraction index in the core. These fibres are composed of several thousands of rods with diameter smaller than incident wavelength. Their optical performance is described with the Maxwell-Garnett effective medium theory. A modification of nanorods distribution or doping level in nanorods allow controlling of chromatic dispersion, polarization and modal properties of the nanostructured fibres. We study an influence of additional microrings in the core on fibre dispersion characteristics. We consider a fibre composed of pure silica nanorods and silica nanorods highly doped with Ge (concentration of GeO2 equals 20% mol). Modification of core internal structure affects electric field distribution in the fundamental mode, and consequently results in changes of its dispersion characteristics. We show that flat, all-normal dispersion characteristics (≈ 2.5 ps/nm/km) in wavelength range from 1.3 up to 2.15 μm can be achieved in the optimized structure. Moreover, within these limits, 1.5 μm to 1.9 μm range was revealed to be ultra-flat (≈ 0.2 ps/nm/km). In contrast to already reported in the literature similar fibres, proposed design is based on fused silica glasses, exhibits spectrally broader and more flat dispersion profile, it is an all-solid construction and it has the effective mode area equal 13μm2 for λ=1.55μm wavelength. Thanks to such characteristics, the fiber allows free from higher order distortions light propagation of highly confined broadband optical pulses, what might find applications in ultrafast optics, or dispersion management systems.
关键词： ultrafast optics,Maxwell-Garnett effective medium theory,chromatic dispersion,nanostructured optical fibres,all-normal dispersion
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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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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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
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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 All-Optical Switching in III-V Semiconductor Resonant Nanostructures
摘要： All-dielectric high-index resonant nanostructures offer plentiful opportunities for tailoring characteristics of scattered radiation. In fact, the low level of ohmic losses at optical frequencies and the presence of pronounced magneto-dipolar modes in scattering spectra of dielectric nanoresonators pave the way to numerous scattering effects that could be employed for many practical applications [1]. To further advance the performance of dielectric nanophotonic devices, it is crucial to make them reconfigurable, i.e. to provide a method to manipulate optical properties of the material that they are made of. The electron-hole injection, carried out by optical means, is a promising solution for this task (Fig. 1A). Direct-gap semiconductors are perfectly suitable for that purpose, because this class of materials retains advantages typical for dielectrics and, at the same time, is defined by smaller bandgap widths, compared to dielectrics. The latter feature significantly decreases a value of the pumping pulse fluence that is required to noticeably change the optical response of a resonant nanostructure. Indeed, it was numerically shown that the change of the trajectory of the probing pulse constituted 20° for an asymmetric dimer comprised of two silicon (Si) spheres of different radii for the energy fluence of the pumping pulse Φ(cid:3020)(cid:3036) = 1.6 mJ cm(cid:2879)(cid:2870) [2]. On the other hand, there is an experimental study of all-optical switching in gallium arsenide (GaAs) metasurface that indicated the change of its reflection coefficient ?(cid:1844) = 0.35 for the fluence Φ(cid:3008)(cid:3028)(cid:3002)(cid:3046) = 0.31 mJ cm(cid:2879)(cid:2870) [3]. Although there are already some numerical results on the light scattering in the asymmetric dimer, it is still urgent to carry out the corresponding experiment. For that purpose, it is important to change the geometry of the system (cylinders instead of spheres) and its material (GaAs in place of Si). The system has an asymmetric scattering profile in the regular regime owing to its asymmetric geometry. The geometry also stipulates the difference in absorption cross-sections of the cylindrical resonators. Because of this difference in absorption, the change of the material’s optical parameters is not equal for the two cylinders. Therefore, under certain conditions, after the pumping of the nanostructure, the scattering diagram becomes symmetric. Our numeric results demonstrate the symmetrization of the indicatrix for the pumping fluence Φ(cid:2869) = 0.9 mJ cm(cid:2879)(cid:2870) (the corresponding change of the probe scattering direction was calculated to be 7°) for the dimer with following geometrical parameters: radii – 85 nm and 90 nm, height – 200 nm, distance between the centers of the disks – 450 nm. The central wavelength of the pulse spectrum was (cid:2019)(cid:2869) = 820 nm. The dimer nanoantenna is an ultrafast optical switch that can be used, for instance, to distribute optical signals between two waveguides in integrated photonic circuits. The design of the switch makes its fabrication compatible with modern technological methods. The all-optical modulation can be observed not only in single asymmetric nanoantennas, but also in phased-array metasurfaces composed of supercells with resonators of the different size. In particular, we considered a metasurface that could control the intensities (i.e. transmission coefficients) in the diffraction orders that are formed after the scattering on the nanostructure. In our experiments, the most pronounced relative change of the transmission coefficient was detected in the first order: ?(cid:1846) (cid:1846) = 9.7% for the fluence of the pumping pulse Φ(cid:2870) = 0.02 mJ cm(cid:2879)(cid:2870) (Fig. 2B). The metasurfaces of that kind can also be used as all-optical switches.
关键词： ultrafast optics,resonant nanostructures,III-V semiconductor,all-optical switching
更新于2025-09-12 10:27:22
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Supercontinuum Generation from a Thulium Ultrafast Fiber Laser in a High NA Silica Fiber
摘要： A broadband supercontinuum is generated from a thulium ultrafast soliton fiber laser in a high numerical aperture silica fiber with low nJ seed pulse energies. Amplification of a thulium based ultrafast soliton ring fiber laser in two customized thulium doped fiber amplifiers provides pulses varying in energy between 1.8 nJ and 13.5 nJ. Coupling these seed pulses into a high numerical aperture silica fiber UHNA 7 of varying length, a systematic study of the impact of pulse energy, pulse duration and nonlinear fiber length is conducted. Based on the normal dispersion, self-phase modulation dominates for lower pump power values and results in a symmetric spectral broadening process. For higher pulse energies, four-wave mixing and Raman scattering contribute to a strong red-shift of the spectrum beyond 2.3 μm. For a fiber length of 20 m of UNHA 7, a broadband supercontinuum spanning from 1.7 μm to 2.33 μm is generated with a 20 dB spectral bandwidth of 502 nm with an output pulse energy of 4.4 nJ, corresponding to an output power of 92 mW. This represents a low seed energy threshold for efficient flat supercontinuum generation at infrared wavelengths.
关键词： Supercontinuum generation,Ultrafast optics,Fiber lasers,Thulium
更新于2025-09-12 10:27:22
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Generation of high-energy and low-repetition rate hybrid pulses from a passively mode-locked Tm-Ho co-doped laser
摘要： This study presents a passively mode-locked Tm-Ho co-doped ?ber laser at around 1840 nm with a low-repetition rate and high pulse energy. The laser delivers pulses at 93 kHz and produces a pulse energy of 18.5 nJ at 0.55 W pump power when the cavity length is 2.21 km. When the pump power is increased, high order of repetition rate outputs are observed. By a comparison of the spectra at various pump power levels indicates that the laser can be operated at hybrid multi-wavelength soliton mode-locking, depending on the pumping intensity. With the increase in pump power, single-wavelength soliton mode-locking and simultaneous of single- and dual-wavelength soliton mode locking are also observed. Besides, the system produces a laser at 1417 nm, which is induced by two-step absorption and the consequent stimulated emission. The low–repetition rate and high–pulse energy ?ber laser at around 1840 nm has potential applications in sensing, processing, and surgery research.
关键词： Optical ?ber lasers,Mode locked lasers,Ultrafast optics
更新于2025-09-12 10:27:22
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Theoretical Design of a Pump-Free Ultrahigh Efficiency All-Optical Switching Based on a Defect Ring Optical Waveguide Network
摘要： A theoretical design of a defect ring optical waveguide network is proposed to construct a pump-free ultrahigh efficiency all-optical switch. This switch creates ultrastrong photonic localization and causes the nonlinear dielectric in the defect waveguide to intensely respond. At its ON state, this material defect without Kerr response helps to produce a pair of sharp pass bands in the transmission spectrum to form the dual channel of the all-optical switch. When it is switched to its OFF state, the strong Kerr response induced refractive index change in the high nonlinear defect waveguide strongly alters the spectrum, leading to a collapse of the dual channels. Network equation and generalized eigenfunction method are used to numerically calculate the optical properties of the switch and obtain a threshold control energy of about 2.90 zJ, which is eight orders of magnitude lower than previously reported. The switching efficiency/transmission ratio exceeds 3×1011, which is six orders of magnitude larger than previously reported. The state transition time is nearly 108 fs, which is approximately two orders of magnitude faster than the previously reported shortest time. Furthermore, the switch size can be much smaller than 2.6 μm and will be suitable for integration.
关键词： ultrafast optics,pump-free,all-optical switching,ultrahigh efficiency,nonlinear optics,waveguide network
更新于2025-09-11 14:15:04