Effects of inhomogeneous laser field in time and space on the generation of broad spectral continuum and ultrashort attosecond pulse

2020 ◽  
Vol 34 (13) ◽  
pp. 2050131
Author(s):  
H. Liu ◽  
L. Q. Feng ◽  
R. M. Sani
Keyword(s):  
Laser Field ◽  
Ionization Probability ◽  
Time And Space ◽  
Harmonic Emission ◽  
High Order Harmonic ◽  
Resonance Enhancement ◽  
Attosecond Pulses ◽  
The Difference ◽  
He Atom ◽  
Frequency Chirping

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.

High-order harmonic emission from a three-level atom in a laser field

1999 ◽  
Vol 46 (5) ◽  
pp. 743-754 ◽  
Author(s):  
Pasquale Caldara ◽  
Emilio Fiordilino
Keyword(s):  
Laser Field ◽  
High Order ◽  
Harmonic Emission ◽  
High Order Harmonic ◽  
Level Atom

High-order harmonic generation with a single-color mid-infrared laser field by frequency-chirping

2019 ◽  
Vol 33 (13) ◽  
pp. 1950122 ◽  
Author(s):  
Yunhui Wang ◽  
Dandan Song ◽  
Qiang Zuo ◽  
Hong Wu ◽  
Zhihong Yang
Keyword(s):  
Harmonic Generation ◽  
Laser Field ◽  
Infrared Laser ◽  
Pulse Generation ◽  
High Order ◽  
Time Dependent ◽  
Mid Infrared ◽  
High Order Harmonic ◽  
Isolated Attosecond Pulse ◽  
Frequency Chirping

By numerically solving the time-dependent Schrödinger equation for helium atoms in a single mid-infrared laser field, we explore the frequency-chirping effect of laser field on high-order harmonic and isolated attosecond pulse generation. One or two ultrabroad supercontinuum harmonic plateaus can be controlled through modulating the laser field frequency by a small time-dependent signal. Under the best chirping condition, an ultrashort 2.2 as pulse can be obtained by Fourier transformation with the bandwidth of 782 eV. Furthermore, we explain the harmonic generation physical mechanisms by classical ionizing and returning energy maps and time–frequency analyzes.

Temporal confinement and enhancement of high-order harmonic emission with a synthesized laser field

2007 ◽  
Vol 75 (5) ◽  
Author(s):  
Hui Xiong ◽  
Ruxin Li ◽  
Zhinan Zeng ◽  
Yinghui Zheng ◽  
Yan Peng ◽  
...  
Keyword(s):  
Laser Field ◽  
High Order ◽  
Harmonic Emission ◽  
High Order Harmonic

HIGH-ORDER HARMONIC GENERATION OF HYDROGEN IN INTENSE LASER FIELD AND STRONG MAGNETIC FIELD

2004 ◽  
Vol 15 (04) ◽  
pp. 493-506
Author(s):  
H. X. QIAO ◽  
Y. C. ZOU ◽  
Z. J. ZHANG
Keyword(s):  
Magnetic Field ◽  
Strong Magnetic Field ◽  
Laser Field ◽  
Pseudospectral Method ◽  
Ionization Probability ◽  
High Order ◽  
Intense Laser ◽  
Intense Laser Field ◽  
High Order Harmonic ◽  
The Magnetic Field

An effective one-dimensional model approach combining time-dependent pseudospectral method and Taylor expansion [Haoxue Qiao et al., Phys. Rev. A65, 063403 (2002)] is generalized to study a real hydrogen atom in an intense laser field. High-order harmonic generations are calculated in several cases of different laser field parameters. The ionization probability is also calculated. The influence of the strong magnetic field on harmonic generations is investigated. It is found that the plateau of high harmonics can be extended by the magnetic field and the cutoff order increases with the increase of the field intensity.

Improvement of High-Order Harmonic Generation Via Controlling Multiple Acceleration–Recombination Process

2019 ◽  
Vol 74 (7) ◽  
pp. 561-571 ◽  
Author(s):  
Yi Li ◽  
Li-Qiang Feng ◽  
Yan Qiao
Keyword(s):  
Harmonic Generation ◽  
Laser Field ◽  
High Order ◽  
Recombination Process ◽  
Half Cycle ◽  
High Order Harmonic Generation ◽  
Water Window ◽  
High Order Harmonic ◽  
Window Region ◽  
Frequency Chirping

AbstractThe multiple acceleration–recombination process in high-order harmonic generation (HHG) has been investigated and discussed. Generally, the HHG can be explained through the ionization–acceleration–recombination process in each half-cycle waveform of the laser field. In this article, through the waveform control via the two-colour frequency-chirping laser field, the multiple acceleration–recombination process of the free electron in a specific “W” waveform structure can be found, which will lead to the larger emitted photon energies. Moreover, with the optimization of this “W” waveform by changing the frequency chirps, the carrier envelope phases, and the delay time, not only the efficiency of HHG can be enhanced compared with that from the original chirp-free pulse, but also the larger harmonic cutoff can be obtained. Further, with the assistance of the unipolar pulses, the cutoff and the efficiency of HHG can be further improved, showing a water window spectral continuum with the intensity enhancement of 66 times. As a result, by properly superposing some selected harmonics on the spectral continuum, three intense 38-as pulses in the water window region can be obtained.

Isolated attosecond pulse generation from different frequency-chirping combined fields

2019 ◽  
Vol 33 (21) ◽  
pp. 1950241
Author(s):  
Hui Liu ◽  
Hang Liu ◽  
Liqiang Feng
Keyword(s):  
Laser Field ◽  
Harmonic Spectrum ◽  
Higher Order ◽  
Pulse Generation ◽  
Attosecond Pulse ◽  
Middle Region ◽  
Chirped Pulse ◽  
High Order Harmonic ◽  
Isolated Attosecond Pulse ◽  
Frequency Chirping

Generation of high-order harmonic spectrum and isolated attosecond pulse (IAP) from frequency-chirping combined field has been investigated. It is found that by adding the middle-chirp form of the laser field, the extension of the harmonic cutoff comes from the middle region of the laser field. However, the intensity of the higher-order spectral continuum is very low. By adding the asymmetric negative chirp form of the laser field, the extension of the harmonic cutoff is attributed to the falling region of the laser field. Moreover, the intensity of the higher-order spectral continuum presents similar value as that produced from the chirp-free pulse. Further, by properly adding a second controlling pulse (i.e., infrared field or ultraviolet pulse) into the fundamental chirped pulse, the intensity of the harmonic spectrum can be enhanced by 2–3 and 1–2 orders of magnitudes for the cases of the middle-chirp form and the asymmetric negative chirp form, respectively. Finally, by using the best laser conditions, a series of isolated attosecond pulses with the durations of 38 as can be produced.

Time and space waveform optimization to extend the harmonic cutoff and to produce the water window single attosecond pulse

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Liqiang Feng ◽  
Quan Yuan
Keyword(s):  
Attosecond Pulse ◽  
Space Region ◽  
Time And Space ◽  
Harmonic Intensity ◽  
Harmonic Emission ◽  
Water Window ◽  
Waveform Optimization ◽  
High Order Harmonic ◽  
Unipolar Pulse ◽  
Time Region

Abstract Based on the three-step theory of high-order harmonic generation, the harmonic cutoff is very sensitive to the few-cycle laser waveform in both time and space regions. Therefore, in this paper, we propose the method to control the harmonic cutoff and to produce the water window attosecond pulse through the optimization of time and space waveform. It is found that, in the time region, by properly choosing the delay and phase of the few-cycle two-color pulse, not only the harmonic intensity is enhanced, but also the quantum path of the harmonic emission can be controlled. Further, with the introduction of the 3rd pulse (i.e., the infrared pulse or the unipolar pulse), the harmonic cutoff from the single harmonic emission peak can be extended, showing a water window harmonic plateau. In the space region, by using the positive spatial inhomogeneous effect, the harmonic cutoff from the basic two-color waveform can also be extended, which leads to a water window spectral continuum. Finally, by Fourier transformation of harmonics during the water window region, the ultrashort single 29 as pulses can be obtained.

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