Intense Isolated Short Attosecond Pulse Generation from a Coherent Superposition State in a Spatially Inhomogeneous Field

2018 ◽  
Vol 73 (4) ◽  
pp. 303-313
Author(s):  
Gangtai Zhang ◽  
Tingting Bai
Keyword(s):  
Excited States ◽  
Harmonic Spectrum ◽  
Pulse Generation ◽  
Spatial Inhomogeneity ◽  
Inhomogeneous Field ◽  
Superposition State ◽  
Initial State ◽  
Coherent Superposition ◽  
Spatially Inhomogeneous ◽  
Attosecond Pulse Generation

AbstractWe theoretically present an efficient method of generating an intense isolated short attosecond (as) pulse in a spatially inhomogeneous field. It is shown that this spatiotemporally combined field can significantly extend the harmonic cut-off and enhance the harmonic efficiency when the initial state is a coherent superposition of the ground and excited states. Then, a highly efficient continuum spectrum with an extremely wide bandwidth is directly generated. Due to the introduction of the spatial inhomogeneity, the short path is selected and the long one is removed; as a result, an intense isolated 17.3-as pulse is obtained straightforwardly. In addition, we also investigate the influences of the parameters including the population of the excited state, spatial inhomogeneity, carrier–envelope phase, pulse duration, and intensity on the harmonic spectrum.

High-order harmonic and attosecond pulse generations from Rydberg state driven by the spatially inhomogeneous field

2017 ◽  
Vol 31 (04) ◽  
pp. 1750029 ◽  
Author(s):  
Liqiang Feng ◽  
Yi Li ◽  
Fanshun Meng ◽  
Hang Liu ◽  
R. S. Castle
Keyword(s):  
Excited State ◽  
Rydberg State ◽  
Attosecond Pulse ◽  
High Order ◽  
Inhomogeneous Field ◽  
Initial State ◽  
Coherent Superposition ◽  
The Third ◽  
High Order Harmonic ◽  
Spatially Inhomogeneous

High-order harmonic spectra and attosecond pulse generation from Rydberg atom (He[Formula: see text]) driven by the spatially inhomogeneous field have been theoretically investigated. (i) Firstly, with an electron initially in a single excited Rydberg state (nth), the harmonic yield can be enhanced due to the decreased ionization potential, and a maximum enhancement can be obtained when the initial state is prepared as the third excited state (n = 3). However, the low cutoff energy from the excited state is unbeneficial to the generation of the higher photon pulse. Thus, with the further introduction of the laser chirp, not only the harmonic cutoff is extended, but also the harmonic modulation is reduced. As a result, five super-bandwidths from 63 eV to 267 eV can be found. (ii) Secondly, by preparing the initial state as a coherent superposition of excited state, the harmonic yield can be further enhanced, especially for the coherent superposition of the first and the third (n = 1 + 3) and the second and the fourth (n = 2 + 4) excited states, the harmonic yield is enhanced by 4–8 orders of magnitude compared with the case of the single ground initial state. Furthermore, by properly adding the laser pulse into the spatially inhomogeneous region (gap center [Formula: see text] a.u.) from left [Formula: see text] to right [Formula: see text], much higher cutoff energies can be obtained in the left region. As a consequence, two super-bandwidths of 248 eV and 496 eV can be obtained. Finally, by properly superposing the harmonics, a series of sub-25-as pulses with intensity enhancement of 5–8 orders of magnitude 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.

Isolated attosecond pulses generation from coherent superposition state of helium ion in static electric fields and spatial nonhomogeneous fields

2016 ◽  
Vol 30 (31) ◽  
pp. 1650229 ◽  
Author(s):  
Hao Liu ◽  
Zhengzhong Zhang ◽  
Yangjiang Wu ◽  
Shicheng Jiang ◽  
Chao Yu
Keyword(s):  
Electric Fields ◽  
Harmonic Generation ◽  
Harmonic Spectrum ◽  
High Order ◽  
High Order Harmonic Generation ◽  
Initial State ◽  
Fundamental Field ◽  
Coherent Superposition ◽  
High Order Harmonic ◽  
Helium Ion

We present a systematic study of high-order harmonic generation (HHG) from helium ion with the initial state prepared as a coherent superposition of electronic ground state and an excited state. As a result, the conversion efficiency of the harmonic spectrum is significantly enhanced. When we add a static electric field in fundamental field, the supercontinuum region of the harmonic spectrum is distinctly extended and an isolated 100 as pulse can be generated. Moreover, we use a spatial nonhomogeneous field to increase the cutoff energy in high-order harmonic generation spectrum, which can be extended to about 700 eV, and an isolated 50 as pulse can be obtained directly by the superposition of the supercontinuum harmonics.

Intense Isolated Ultrashort Attosecond Pulse Generation in a Multi-Cycle Three-Colour Laser Field

2014 ◽  
Vol 69 (12) ◽  
pp. 673-686 ◽  
Author(s):  
Gang-Tai Zhang
Keyword(s):  
Laser Field ◽  
High Efficiency ◽  
Harmonic Spectrum ◽  
Pulse Generation ◽  
Attosecond Pulse ◽  
Smooth Structure ◽  
Single Quantum ◽  
Isolated Attosecond Pulse ◽  
Attosecond Pulse Generation ◽  
Selection Of

AbstractAn efficient method for generating an intense isolated ultrashort attosecond pulse is presented theoretically. By adding a 267 nm controlling pulse to a multi-cycle two-colour field, not only the spectral cutoff and the yields of the harmonic spectrum are evidently enhanced, but also the selection of the single quantum path is realised. Then a high-efficiency supercontinuum with a 504 eV bandwidth and smooth structure is obtained, which enables the production of an intense isolated 30 as pulse. In addition, the influences of the laser parameters on the supercontinuum and isolated attosecond pulse are investigated.

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