Control of the half-cycle harmonic emission process for generating the intense and ultrashort single attosecond pulses (SAPs)

2020 ◽  
Vol 75 (11) ◽  
pp. 903-911
Author(s):  
Li-Qiang Feng ◽  
Li Liu
Keyword(s):  
Resonance Ionization ◽  
Half Cycle ◽  
Generation Process ◽  
Harmonic Intensity ◽  
Emission Process ◽  
Chirped Pulse ◽  
Attosecond Pulses ◽  
Higher Harmonic ◽  
Photon Resonance ◽  
Positive Half

AbstractIn this paper, the half-cycle harmonic generation process has been controlled by using the asymmetric inhomogeneous chirped pulse combined with the ultraviolet (UV) pulse. It is found that by properly optimizing the chirps and chirp delays of the fundamental two-color pulse, the optimal negative and positive half-cycle laser profiles for the harmonic cutoff extension can be obtained. Further, with the introduction of the negative and positive inhomogeneous effect, respectively, the harmonic cutoff from the negative and positive half-cycle laser profiles can be further improved. Next, with the assistance of the UV pulse, the harmonic intensity can be enhanced due to the UV resonance ionization. Moreover, the single and double UV photon resonance ionizations are much better for generating the higher harmonic intensity. As a result, the stronger and broader harmonic plateaus with the larger harmonic cutoff can be obtained, which can support the generation of the high-intensity ultrashort attosecond pulses with the pulse durations of sub-45 as.

Generation of the high-intensity single harmonic energy peak and attosecond pulse by using resonance ionization schemes from atoms and molecules

2020 ◽  
pp. 2150022
Author(s):  
Xiaodan Jing ◽  
Liqiang Feng ◽  
Li Liu ◽  
John Mccain ◽  
Yi Li
Keyword(s):  
Molecular System ◽  
Attosecond Pulse ◽  
Resonance Ionization ◽  
Half Cycle ◽  
Harmonic Intensity ◽  
Molecular Systems ◽  
Unipolar Pulse ◽  
Energy Peak ◽  
Attosecond Pulses ◽  
Time Region

The lower harmonic intensity is still the reason that limits the application of attosecond pulse. Thus, in this paper, on the basis of resonance ionization schemes, we propose the effective methods to improve the harmonic intensity of atomic and molecular systems. For atomic system (i.e. He atom), with the combination of chirped-UV pulse, not only the harmonic cutoff can be extended, but also the harmonic intensity can be enhanced, caused by the UV resonance ionization between ground state and excited state. As a result, the single harmonic energy peak (HEP) with the higher intensity and higher emitted photon energy can be obtained, which can support the attosecond pulses shorter than 40 as. For the molecular system (i.e. [Formula: see text] and [Formula: see text]), by properly choosing the pulse duration of the fundamental pulse, the time region of charge resonance enhanced ionization (CREI) can be well controlled. Therefore, the maximum HEP with the higher intensity can be obtained. Second, by properly adding a half-cycle unipolar pulse, the selected maximum HEP in the CREI region can be further extended. Thus, an intense and broad spectral region can be produced, which can generate the attosecond pulses with durations of 36[Formula: see text]as.

Generation of intense spectral continuum and isolated attosecond pulse by selecting single harmonic emission peak

2019 ◽  
Vol 33 (35) ◽  
pp. 1950444
Author(s):  
Liqiang Feng ◽  
Yi Li
Keyword(s):  
Pulse Duration ◽  
Laser Intensity ◽  
Attosecond Pulse ◽  
Resonance Ionization ◽  
Lower Intensity ◽  
Harmonic Intensity ◽  
Chirped Pulse ◽  
Harmonic Emission ◽  
Pulse Intensity ◽  
Isolated Attosecond Pulse

Generally, due to the interference of different harmonic emission peaks (HEPs), the intensity of high-order harmonic spectrum cannot keep enhancing as the pulse intensity increases. Thus, in this paper, a potential method to obtain an intense spectral continuum and isolated attosecond pulse (IAP) by selecting single HEP has been theoretically investigated. First, we choose the harmonic cutoff and the harmonic intensity from the optimal single-color laser intensity as the referenced values. Next, by properly choosing a lower-intensity negative chirped pulse, we see that the harmonic cutoff from this field is similar as that from the referenced field. Moreover, the spectral continuum is contributed by single HEP. However, the intensity of the spectral continuum from the negative chirped pulse is lower than that from the referenced field. As the pulse duration of the chirped pulse increases, the similar harmonic cutoff can also be found by using a much lower-intensity negative chirped pulse. However, the intensity of the spectral continuum is decreased compared with that from the shorter chirped pulse duration. Further, with the introduction of an IR or UV controlling pulse, the intensity of the spectral continuum can be enhanced up to the referenced value. Moreover, the longer the pulse duration of the controlling pulse is used, the lower the controlling pulse intensity is needed. Also, due to the UV resonance ionization, much lower UV intensity is needed to enhance the harmonic yield compared with that for adding IR controlling pulse case. All in all, the total laser intensity of the combined field (the fundamental pulse + the controlling pulse) is lower than that of the referenced field. Most importantly, the signal of the spectral continuum is only coming from single HEP, which can support the generations of intense IAPs with the durations of 30 as.

Nonlinear chirp combination effect on the improvement of high harmonic spectra and attosecond pulses

2021 ◽  
pp. 2150225
Author(s):  
Li-Qiang Feng ◽  
Xiao-Dan Jing ◽  
Yan Qiao ◽  
John McCain ◽  
Quan Yuan ◽  
...  
Keyword(s):  
High Harmonic ◽  
Harmonic Spectrum ◽  
Combination Effect ◽  
Harmonic Intensity ◽  
Chirped Pulse ◽  
Intensity Enhancement ◽  
Attosecond Pulses

The effect of nonlinear chirp combination on the enhancement of harmonic cutoff and harmonic intensity has been investigated by using a two-color chirped pulse. It is found that with the combination of 2-order chirp form, the strongest intensity enhancement of harmonic spectrum can be found. While, with the combination of 2-order and 3-order chirp forms, the largest cutoff extension of the harmonic spectrum can be obtained. Finally, by properly using the harmonic spectra driven by the above two kinds of combined pulses, the single attosecond pulses (SAPs) of 43 as and 33 as can be generated.

Multi-Photon Resonance Ionization of Emitted Particles

1986 ◽  
pp. 90-93 ◽  
Author(s):  
G. A. Schick ◽  
J. P. Baxter ◽  
J. Subbiah-Singh ◽  
P. H. Kobrin ◽  
N. Winograd
Keyword(s):  
Resonance Ionization ◽  
Photon Resonance

Saturated Two-Photon Resonance Ionization ofHe(2S1)

1975 ◽  
Vol 35 (2) ◽  
pp. 82-85 ◽  
Author(s):  
G. S. Hurst ◽  
M. G. Payne ◽  
M. H. Nayfeh ◽  
J. P. Judish ◽  
E. B. Wagner
Keyword(s):  
Resonance Ionization ◽  
Two Photon ◽  
Photon Resonance

Attosecond XUV sources generation from polarized gating two-color chirped pulse

2015 ◽  
Vol 29 (21) ◽  
pp. 1550111 ◽  
Author(s):  
Liqiang Feng ◽  
Hang Liu ◽  
Tianshu Chu
Keyword(s):  
High Order ◽  
Promising Method ◽  
Polarization Angle ◽  
Single Quantum ◽  
Experimental Realization ◽  
Chirped Pulse ◽  
Laser Parameters ◽  
High Order Harmonic ◽  
Attosecond Pulses ◽  
Cycle Pulse

A promising method to generate the attosecond XUV sources from the high-order harmonic has been theoretically presented by controlling the polarized gating two-color chirped pulse. The results show that with the introduction of the chirps, the harmonic has been remarkably extended. Moreover, the harmonic interferences are very sensitive to the polarization angle between the two lasers. Particularly, when the polarization angle is equal to [Formula: see text], the supercontinuum with a single quantum path contribution is achieved, and a series of isolated attosecond pulses with the duration of 33 as are directly obtained. Further, by testing the influences of other laser parameters on the supercontinuum, we found that this polarized two-color chirped scheme can also be achieved in the multi-cycle pulse region, which is much better for experimental realization.

Spatial distribution and quantum trajectory control of the molecular harmonic spectra

2016 ◽  
Vol 25 (04) ◽  
pp. 1650053 ◽  
Author(s):  
Hang Liu ◽  
Rich-Samuel Castle ◽  
Wenliang Li ◽  
Liqiang Feng
Keyword(s):  
Spatial Distribution ◽  
Physical Mechanism ◽  
Trajectory Control ◽  
Quantum Trajectory ◽  
Half Cycle ◽  
Time Frequency ◽  
Positive Formula ◽  
Gold Nanostructure ◽  
Higher Harmonic ◽  
Cycle Pulse

Spatial distribution and quantum trajectory control of the molecular harmonic spectra from H[Formula: see text] are theoretically investigated through the combination of a few-cycle 800[Formula: see text]nm pulse and a half-cycle pulse. Results show that by properly adding the half-cycle pulse, the harmonic cutoffs from the recombination process are extended, and the harmonic intensities from the positive-[Formula: see text] direction are suppressed. Moreover, as the internuclear distance increased, the modulations on the harmonic spectra are reduced. The time-dependent wave function and the time-frequency analyses of the harmonic spectra are shown to explain the above physical mechanism. Further, by adding the laser pulse to the bowtie-shaped gold nanostructure separated by an air gap [Formula: see text][Formula: see text]nm, much higher harmonic cutoff order can be obtained in the positive-[Formula: see text] region. Finally, two isolated attosecond pulses with the full width at half maximum of 34as and 31as are obtained.

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