- 标题
- 摘要
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Resonance Enhancement in Laser-Produced Plasmas (Concepts and Applications) || Front Matter
摘要： The motivation in writing this book is to show the most recent findings of newly emerged field of resonance-enhanced high-order harmonic generation (HHG) using the laser pulses propagating through the narrow and extended laser-produced plasma plumes. It becomes obvious that the developments in this field are aimed for improvement of harmonic yield through precise study of resonance effects during fine-tuning of driving pulses to the resonances. The purpose of writing this book is to acquaint the readers with the most advanced, recently developed methods of plasma harmonics generation at the conditions of coincidence of some harmonics, autoionizing states, and some ionic transitions possessing strong oscillator strengths. This book demonstrates how one can improve the plasma harmonic technique using this approach.
关键词： extreme ultraviolet,plasma harmonics,laser-produced plasmas,high-order harmonic generation,resonance enhancement,XUV,nonlinear optics,HHG
更新于2025-09-19 17:13:59
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Effects of inhomogeneous laser field in time and space on the generation of broad spectral continuum and ultrashort attosecond pulse
摘要： The inhomogeneous effects of laser field in time and space on the generations of high-order harmonic spectra and attosecond pulses from He atom have been investigated with the assistance of the frequency-chirping technique and the metallic nanostructure. We find that in different combinations of chirps and spatial inhomogeneous effects, not only can the harmonic cutoff be extended, but the single harmonic emission peak (HEP) can also be selected to contribute to the spectral continuum. In detail, with the combinations of (i) symmetric chirp in frequency and positive inhomogeneous effect in space or (ii) asymmetric down chirp in frequency and negative inhomogeneous effect in space, two broad spectral continua with bandwidths of 496 eV and 480 eV can be obtained. Further, by properly adding IR or UV controlling pulse, the harmonic emission efficiency can be enhanced by several orders of magnitude. The enhancement of harmonic yield from adding UV pulse is higher than that from adding IR pulse. Moreover, the difference of harmonic enhancement between UV combined field and IR combined field is much more obvious at lower controlling laser intensity. Through analyzing the ionization probability, we find that the higher enhancement of harmonic yield from UV combined field is because of UV-resonance-enhancement-ionization between the ground state and the excited state of He atom. Finally, by properly superposing some harmonics, a number of attosecond pulses with pulse durations of 45 as can be obtained.
关键词： frequency-chirping technique,High-order harmonic generation,two-color field,inhomogeneous effect in space,ultrashort attosecond pulse
更新于2025-09-19 17:13:59
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Selective enhancement of single-order and two-order harmonics from He atom via two-color and three-color laser fields
摘要： An effective method to achieve the selective enhancement of single-order and two-order harmonics from He atom has been proposed through laser waveform control of two-color and three-color laser fields. Firstly, with the optimization of ω-2ω two-color laser waveform, not only the wavelength tunable single-order harmonic (i.e. from 182th order to 328th order) can be enhanced by 17 times compared with the neighbor harmonics, but also the enhancement of two-order harmonics can also be obtained. Theoretical analyses show that the enhancement of the specific harmonics is coming from the folded structure on the short quantum path of the harmonic emission peak. Detail analyses show that the above folded structure happens in the reversed sub-peak region of the half-cycle laser waveform, where the deceleration and further acceleration of the free electron can be found in this structure. Moreover, this structure is dependent on the pulse duration of the controlling pulse. However, it is not very sensitive to the wavelength of the controlling pulse. Further, by properly adding a 3ω pulse, not only the efficiency of spectral continuum can be enhanced by 300 times compared with that from the two-color field, but also the generation of single-order harmonic with the intensity enhancement of 20 times can be found. Furthermore, the enhancement of the harmonic spectrum can also be achieved when using the 4ω or 6ω controlling pulses.
关键词： Selective enhancement of two-order harmonics,Two-color and three-color combined fields,Selective enhancement of single-order harmonics,High-order harmonic generation,Laser waveform control
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) - Sub-20 fs ? 10.5 W Visible Pulse Generation from Yb-Doped Fiber Laser
摘要： High-power high-repetition rate femtosecond ytterbium-doped fiber lasers offer new perspectives in femtochemistry, solid-state physics and strong field physics. In particular, high-order harmonic generation (HHG) driven by Yb-fiber laser has demonstrated high photons flux in extreme ultraviolet (XUV) spectral range [1,2]. Shortening the laser pulse improves the achievable time resolution in pump-probe experiments and also the efficiency and the spectral extent of HHG (cutoff wavelength). However, the gain bandwidth of the Yb:fiber limits the pulse duration in the 250 fs - 130 fs range. To solve this issue, nonlinear pulse compression experiments using Yb:fiber lasers have been carried out at the fundamental wavelength (1030 nm) to downscale the pulse duration in the 10 fs range [3,4]. On the other hand, so far the highest reported XUV photons flux up to milliwatt-class has been obtained at 515 nm driving wavelength with 11W - 85 fs pulses [5]. While frequency doubling an ultrashort (< 30 fs) pulse requires a trade-off between efficiency and pulse duration lengthening, we present in this work an efficient and high power sub-20 fs visible laser source based on the second harmonic generation (SHG) of a high energy Yb-doped femtosecond fiber laser followed by a nonlinear compression stage in a krypton-filled capillary.
关键词： femtosecond ytterbium-doped fiber lasers,nonlinear pulse compression,krypton-filled capillary,second harmonic generation,high-order harmonic generation
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) - Comparative Study of High Order Harmonic Generation in Monolayer-Thick Semiconductors
摘要： In this contribution we report on the results of an experimental comparative study of high order harmonic generation (HHG) from strong mid-IR femtosecond laser pulses in two-dimensional (2D) materials consisting of a single layer. Beside their promising application in electronics and photonics, these materials allow to study microscopic light-condensed-matter interaction on the atomic scale. HHG in 2D materials, in comparison to a bulk, have several distinct qualitative features: single atom layer essentially excludes propagation effects and minimizes absorption, whereas weak charge screening results in significantly higher exciton binding energy. Here we report on comparative study of intensity and polarization dependence of HHG in polycrystalline single layers of MoS2 and WS2.
关键词： WS2,MoS2,mid-IR femtosecond laser pulses,2D materials,high order harmonic generation
更新于2025-09-16 10:30:52
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Polarization of high-order harmonic generation in oriented molecules with intense ultrashort laser pulses
摘要： Using numerical solutions of the time-dependent Schr?dinger equation we show that in oriented molecules one can control the polarization of molecular high-order harmonic generation (MHOHG) by intense linearly polarized pulses. For oriented triangular molecules, H3+/H32+, one obtains even-order harmonics perpendicular to the laser polarization, whereas all odd-order harmonics have the same polarization as the laser polarization. For H2+/H2 we show that only odd-order harmonics are generated for any orientation and their polarization is nearly parallel to the molecular axis. We describe these phenomena based on perturbation theory. Redshifts of the MHOHG spectra occur due to laser induced electron localization in non-Born-Oppenheimer dissociating molecules, reflecting the effect of nuclear dynamics. The numerical results illustrate the sensitivity of harmonic polarization to molecular geometry and nuclear dynamics.
关键词： oriented molecules,ultrashort laser pulses,perturbation theory,nuclear dynamics,high-order harmonic generation,polarization
更新于2025-09-16 10:30:52
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Controlling circularly polarized high-order harmonic generation in molecules by intense tricircular laser pulses
摘要： We present a scheme to control circularly polarized high-order harmonic generation (HHG) in molecules, the source of extreme ultraviolet and x-ray pulses, by multiple frequency co- and counter-rotating circularly polarized laser pulses. Simulations are performed on the oriented single electron molecular ions with cyclic equilateral geometry, H2+ 3 , as benchmark models, by numerically solving time-dependent Schr?dinger equations. Results show that circularly polarized HHG can be produced with extended harmonic order cutoffs, which depend on the intensity ratio of ?elds and the ?eld-molecule symmetry. We describe the laser induced electron dynamics in a rotating frame to examine recollision dynamics and Coriolis effects. The resulting modulation of HHG spectra arises from a combination of two bicircular ?elds with counter-rotating and co-rotating components. It is also found that harmonic polarization is a function of the pulse frequencies and helicities, illustrating the importance of matching the ?eld-molecule symmetry. The results in principle illustrate a method for controlling circular polarization properties of harmonics in molecules.
关键词： tricircular laser pulses,molecules,electron dynamics,high-order harmonic generation,circularly polarized
更新于2025-09-16 10:30:52
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The isotopic dependence and influence of driving laser intensity on the harmonic yields of diatomic molecule ions X2+
摘要： The harmonic yields from X2+ (including H2+, D2+ and T2+) driven by 800 nm laser with different laser intensities and pulse durations have been studied. At shorter pulse duration, the harmonic yields of X2+ follows as H2+ > D2+ > T2+, and the intensity difference is decreased as laser intensity increases. At longer pulse duration, the harmonic yields of X2+ follows as T2+ > H2+ > D2+, and the intensity difference is increased as laser intensity increases. Furthermore, the harmonic yield from X2+ can also be modulated by laser chirps. Finally, the physical mechanism is displayed clearly in ionization probability, internuclear distance and time-profile of harmonic emission.
关键词： High-order harmonic generation,Isotope effect,Diatomic molecule X2+,Harmonic yields from X2+
更新于2025-09-12 10:27:22
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irradiated by a co-rotating two-color circularly polarized laser field
摘要： The high-order harmonic generation process of H2+ in a co-rotating two-color circularly polarized laser pulse was investigated by numerically solving the time-dependent Schr?dinger equation. Compared with the target of the atom, the harmonic intensity of H2+ is remarkably enhanced. Moreover, the harmonic intensity of H2+ approaches its maximum when the electric field amplitude ratio of the fundamental frequency and the second one is approximately 1:2.3. By analyzing the evolution of the time-dependent wave packets, the enhancement of harmonic intensity may be attributed to an increase in the probability of the ionized electron recolliding with the parent ion. In addition, the dependence of harmonic intensity on the internuclear distance and the alignment angle of H2+ is explored. We found that the ellipticity of the particular harmonic order changes with the molecular alignment angle, which provides a chance to generate an extreme ultraviolet coherent light pulse with controllable polarization.
关键词： time-dependent Schr?dinger equation,H2+,harmonic intensity,alignment angle,extreme ultraviolet coherent light pulse,controllable polarization,co-rotating two-color circularly polarized laser field,internuclear distance,high-order harmonic generation
更新于2025-09-12 10:27:22
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Phase jump in resonance harmonic emission driven by strong laser fields
摘要： We present a theoretical investigation of the multiphoton resonance dynamics in the high-order-harmonic generation (HHG) process driven by a strong driving cw field along with a weak control harmonic field. The Floquet theorem is employed to provide a nonperturbative and exact treatment of the interaction between a quantum system and the combined driving and control fields. Phase jumps are observed when sweeping across the resonance by varying the frequency or intensity of the driving field. The phase variation as a function of the frequency and intensity of the driving field allows us to determine the intensity dependence of the transition energy of quantum systems.
关键词： high-order harmonic generation,phase jump,stark-shifted transition energy
更新于2025-09-12 10:27:22