Waveform control in generations of intense water window attosecond pulses via multi-color combined field

2019 ◽  
Vol 33 (13) ◽  
pp. 1950130 ◽  
Author(s):  
Liang Li ◽  
Mian Zheng ◽  
R. Liqiang Feng ◽  
Yan Qiao
Keyword(s):  
Half Cycle ◽  
High Order Harmonic Generation ◽  
Initial State ◽  
Water Window ◽  
The Third ◽  
High Order Harmonic ◽  
Waveform Control ◽  
Attosecond Pulses ◽  
Color Field ◽  
Selective Enhancement

The waveform control in the improvements of high-order harmonic generation (HHG) spectra and attosecond pulse signals driven by the two-color and three-color combined fields has been theoretically investigated. (a) The results show that by properly controlling the [Formula: see text]–2[Formula: see text] two-color laser beam (including the modulations of chirps, carrier envelope phases and delay time), either the harmonic cutoff can be extended, showing a water window spectral continuum, or the selective enhancement of the single-order and two-order harmonics can be found. Further, with the introduction of a third controlling field, the efficiency of spectral continuum can be enhanced by two orders of magnitude compared with that from the two-color field. Moreover, the enhancement of HHG is not very sensitive to the frequency of the third field (i.e., the frequency of the third field is chosen to be 3[Formula: see text], 4[Formula: see text] and 6[Formula: see text]). Thus, some water window attosecond pulses with the durations of 60 as can be obtained. (b) Furthermore, the harmonic cutoff can be further extended when using a half-cycle controlling pulse or introducing the inhomogeneous effect of the laser field. Moreover, the efficiency of HHG can be further improved when the initial state is prepared as the superposition state of the ground state and some excited state of He atom. Consequently, a much broader spectral continuum with an intensity enhancement of another two orders of magnitude can be found. Finally, through the Fourier transformation of some spectral continuum, the intense water window attosecond pulses with the durations of 60 as can be produced.

Initial state effect on waveform control of high-order harmonic spectrum and attosecond pulse generation

2021 ◽  
pp. 2150366
Author(s):  
Hang Liu ◽  
Xiaodan Jing ◽  
Yan Qiao ◽  
John McCain ◽  
Liqiang Feng
Keyword(s):  
Harmonic Spectrum ◽  
Pulse Generation ◽  
Attosecond Pulse ◽  
High Order ◽  
High Order Harmonic Generation ◽  
Initial State ◽  
High Order Harmonic ◽  
Waveform Control ◽  
Attosecond Pulses ◽  
Attosecond Pulse Generation

In this paper, the waveform control of high-order harmonic generation and attosecond pulse generation from a different initial state of He atom has been investigated. The results show that (i) by properly controlling the carrier-envelope phases, the time delays and the laser intensities of a 3-color laser pulse, the best waveforms for the harmonic cut-off extension can be found. Although the harmonic cut-offs from the ground initial state and the superposition initial state are almost the same, the harmonic intensities from the superposition initial state are 4 to 5 orders of magnitudes higher than those from the ground initial state. (ii) With the introduction of the inhomogeneous effect, the harmonic cut-offs can be further extended. However, the harmonic intensities from the superposition initial state are remarkably decreased compared with those from the homogeneous pulses, which is unbeneficial to generate the intense attosecond pulses. (iii) When the ground state is chosen to be the initial and with the assistance of the 4th UV pulse, not only the larger harmonic cut-offs can be obtained, but also the stronger harmonic plateaus can be found, which is favorable for producing the intense attosecond pulses. Thus, at the end of this paper, by superposing the harmonics from the best harmonic spectra, the single attosecond pulses with the duration of 36 as can be obtained.

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.

Selection and Enhancement of the Single Harmonic Emission Event in the Water Window Region

2018 ◽  
Vol 73 (11) ◽  
pp. 985-994 ◽  
Author(s):  
Hang Liu ◽  
A. Yuanzi Feng
Keyword(s):  
Fourier Transformation ◽  
Half Cycle ◽  
Laser Polarization ◽  
High Order Harmonic Generation ◽  
Harmonic Emission ◽  
Water Window ◽  
Polarization Gating ◽  
High Order Harmonic ◽  
Window Region ◽  
Cycle Pulse

AbstractThe control of the high-order harmonic generation in the half-cycle region has been investigated by using the improved polarization gating (PG) technology. It is found that by properly controlling the delay time of the PG pulse, the contribution of the harmonic plateau is nearly coming from the single harmonic emission event, which is much better for producing the single attosecond pulses (SAPs). Further, by properly adding an ultraviolet pulse and a half-cycle pulse in the driven laser polarization direction, the harmonic yield can be enhanced and the harmonic cutoff can be extended, showing a high-intensity harmonic plateau covering the whole water window region. Finally, through the Fourier transformation of some selected harmonics, a 35 as SAP in the water window region can be obtained.

scholarly journals Attosecond source generation using polarized gating two-color field combined with unipolar pulse

2016 ◽  
Vol 94 (7) ◽  
pp. 651-658 ◽  
Author(s):  
Liqiang Feng ◽  
Hang Liu
Keyword(s):  
Harmonic Generation ◽  
Extreme Ultraviolet ◽  
Harmonic Spectrum ◽  
High Order ◽  
High Order Harmonic Generation ◽  
Emission Process ◽  
Harmonic Emission ◽  
High Order Harmonic ◽  
Unipolar Pulse ◽  
Color Field

High-order harmonic generation and attosecond extreme-ultraviolet source generation have been theoretically investigated by controlling the two-color polarized gating field combined with the unipolar pulse. The results show that by properly optimizing the polarized two-color field as well as the unipolar pulse, not only is the harmonic cutoff remarkably extended, but the single short quantum path has also been selected to contribute to the harmonic spectrum, resulting in a 313 eV less modulated supercontinuum. Classical and quantum analyses are shown to explain the harmonic emission process. Finally, the proper superposition of harmonics, a series of isolated sub-50 as pulses, can be obtained.

scholarly journals Control of the polarization direction of isolated attosecond pulses using inhomogeneous two-color fields

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Stephen Maina Njoroge ◽  
Hua Yuan ◽  
Kinyua Dickson ◽  
Qingbin Zhang ◽  
Pengfei Lan
Keyword(s):  
Polarization Direction ◽  
Relative Angle ◽  
Water Window ◽  
High Order Harmonic ◽  
Fundamental Pulse ◽  
Wide Range ◽  
Attosecond Pulses ◽  
Linearly Polarized ◽  
Window Region ◽  
And Control

AbstractWe theoretically demonstrate the control of the polarization direction of isolated attosecond pulses (IAPs) with inhomogeneous two-color fields synthesized by an 800-nm fundamental pulse and a 2000-nm control pulse having crossed linear polarizations. The results show that by using the temporally and spatially shaped field, the high-order harmonic generation (HHG) process can be efficiently controlled. An ultra-broad supercontinuum ranging from 150th to 400th harmonics which covers the water window region is generated. Such a supercontinuum supports the generation of a 64-as linearly polarized IAP, whose polarization direction is at about 45° with respect to the x axis. Moreover, we analyze the influence of the inhomogeneity parameters and the relative angle of the fundamental and control pulses on the IAP generation. It is shown that the polarization direction of the IAP can rotate in a wide range approximately from 8° to 90° relative to the x axis when the inhomogeneity parameters and the relative angle vary.

scholarly journals Focusing Properties of High-Order Harmonics

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Maria Hoflund ◽  
Jasper Peschel ◽  
Marius Plach ◽  
Hugo Dacasa ◽  
Kévin Veyrinas ◽  
...  
Keyword(s):  
Extreme Ultraviolet ◽  
Laser System ◽  
High Order ◽  
Harmonic Order ◽  
High Order Harmonic Generation ◽  
High Order Harmonic ◽  
Attosecond Pulses ◽  
Small Focus ◽  
The Individual ◽  
Focusing Properties

Many applications of the extreme ultraviolet (XUV) radiation obtained by high-order harmonic generation (HHG) in gases require a small focus area in order to enable attosecond pulses to reach a high intensity. Here, high-order harmonics generated in Ar with a multiterawatt laser system in a loose focusing geometry are focused to a few micrometers using two toroidal mirrors in a Wolter configuration with a high demagnification factor. Using a knife-edge measurement technique, we determine the position and size of the XUV foci as a function of harmonic order. We show that the focus properties vary with harmonic order and the generation conditions. Simulations, based on a classical description of the harmonic dipole phase and assuming that the individual harmonics can be described as Gaussian beams, reproduce the experimental behavior. We discuss how the generation geometry affects the intensity and duration of the focused attosecond pulses.

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