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Unravelling the dynamical origin of below- and near-threshold harmonic generation of H 2 + in an intense NIR laser field

View Article: PubMed Central - PubMed

ABSTRACT

Recently, the study of near- and below- threshold regime harmonics as a potential source of intense coherent vacuum-ultraviolet radiation has received considerable attention. However, the dynamical origin of these lower harmonics, particularly for the molecular systems, is less understood and largely unexplored. Here we perform the first fully ab initio and high precision 3D quantum study of the below- and near-threshold harmonic generation of molecules in an intense 800-nm near-infrared (NIR) laser field. Combining with a synchrosqueezing transform of the quantum time-frequency spectrum and an extended semiclassical analysis, we explore in-depth the roles of various quantum trajectories, including short- and long trajectories, multiphoton trajectories, resonance-enhanced trajectories, and multiple rescattering trajectories of the below- and near- threshold harmonic generation processes. Our results shed new light on the dynamicalorigin of the below- and near-threshold harmonic generation and various quantum trajectories for diatomic molecules for the first time.

No MeSH data available.


SST time profiles and dynamical phase of the harmonic spectra of .(a) The time profiles of the 29th harmonic (H29, above threshold). The red, green, and blue dots are the corresponding dynamical phases for the peak intensity of the short, long, and multi-rescattering trajectories calculated by the SST, respectively. (b) Same as a, for the time profiles of the 21st harmonic (H21, near threshold). (c) Same as a, for the time profiles of the 17th harmonic (H17, below threshold, nonresonant). (d) Same as a, for the time profiles of the 7th harmonic (H7, below-threshold resonant). The light blue dots are the corresponding dynamical phases of the resonant trajectories. The laser parameters used are the same as those in Fig. 1.
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f5: SST time profiles and dynamical phase of the harmonic spectra of .(a) The time profiles of the 29th harmonic (H29, above threshold). The red, green, and blue dots are the corresponding dynamical phases for the peak intensity of the short, long, and multi-rescattering trajectories calculated by the SST, respectively. (b) Same as a, for the time profiles of the 21st harmonic (H21, near threshold). (c) Same as a, for the time profiles of the 17th harmonic (H17, below threshold, nonresonant). (d) Same as a, for the time profiles of the 7th harmonic (H7, below-threshold resonant). The light blue dots are the corresponding dynamical phases of the resonant trajectories. The laser parameters used are the same as those in Fig. 1.

Mentions: We first consider the time profile and dynamical phases of the 29th harmonic (H29) in Fig. 5a as an example of the harmonics in the above-threshold region, where the tunneling mechanism is dominant. As shown in the figure, there is a major peak followed by several small peaks within each half optical cycle of the time profile. By marking the dynamical phases of these peaks and comparing the corresponding emission times with those of the semiclassical trajectories in Fig. 3a,b, we find that the major peak corresponds to the short trajectories, while the minor ones correspond to the long trajectories and multi-rescattering trajectories. The time profile presents a complex pattern within each half optical cycle, suggesting that in addition to the short and long trajectories, the contribution of multi-rescattering trajectories become significant. In addition, the dynamical phase of the long (green dots) and multi-rescattering(blue dots) trajectories are sensitive to the laser profile (since the travel time for these trajectories are long), whereas those for the short trajectories (red dots) are not (shorter travel time). Similar behavior is observed in our previous atomic studies of the H-atom36, Na-atom37, and Cs-atom24.


Unravelling the dynamical origin of below- and near-threshold harmonic generation of H 2 + in an intense NIR laser field
SST time profiles and dynamical phase of the harmonic spectra of .(a) The time profiles of the 29th harmonic (H29, above threshold). The red, green, and blue dots are the corresponding dynamical phases for the peak intensity of the short, long, and multi-rescattering trajectories calculated by the SST, respectively. (b) Same as a, for the time profiles of the 21st harmonic (H21, near threshold). (c) Same as a, for the time profiles of the 17th harmonic (H17, below threshold, nonresonant). (d) Same as a, for the time profiles of the 7th harmonic (H7, below-threshold resonant). The light blue dots are the corresponding dynamical phases of the resonant trajectories. The laser parameters used are the same as those in Fig. 1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121898&req=5

f5: SST time profiles and dynamical phase of the harmonic spectra of .(a) The time profiles of the 29th harmonic (H29, above threshold). The red, green, and blue dots are the corresponding dynamical phases for the peak intensity of the short, long, and multi-rescattering trajectories calculated by the SST, respectively. (b) Same as a, for the time profiles of the 21st harmonic (H21, near threshold). (c) Same as a, for the time profiles of the 17th harmonic (H17, below threshold, nonresonant). (d) Same as a, for the time profiles of the 7th harmonic (H7, below-threshold resonant). The light blue dots are the corresponding dynamical phases of the resonant trajectories. The laser parameters used are the same as those in Fig. 1.
Mentions: We first consider the time profile and dynamical phases of the 29th harmonic (H29) in Fig. 5a as an example of the harmonics in the above-threshold region, where the tunneling mechanism is dominant. As shown in the figure, there is a major peak followed by several small peaks within each half optical cycle of the time profile. By marking the dynamical phases of these peaks and comparing the corresponding emission times with those of the semiclassical trajectories in Fig. 3a,b, we find that the major peak corresponds to the short trajectories, while the minor ones correspond to the long trajectories and multi-rescattering trajectories. The time profile presents a complex pattern within each half optical cycle, suggesting that in addition to the short and long trajectories, the contribution of multi-rescattering trajectories become significant. In addition, the dynamical phase of the long (green dots) and multi-rescattering(blue dots) trajectories are sensitive to the laser profile (since the travel time for these trajectories are long), whereas those for the short trajectories (red dots) are not (shorter travel time). Similar behavior is observed in our previous atomic studies of the H-atom36, Na-atom37, and Cs-atom24.

View Article: PubMed Central - PubMed

ABSTRACT

Recently, the study of near- and below- threshold regime harmonics as a potential source of intense coherent vacuum-ultraviolet radiation has received considerable attention. However, the dynamical origin of these lower harmonics, particularly for the molecular systems, is less understood and largely unexplored. Here we perform the first fully ab initio and high precision 3D quantum study of the below- and near-threshold harmonic generation of molecules in an intense 800-nm near-infrared (NIR) laser field. Combining with a synchrosqueezing transform of the quantum time-frequency spectrum and an extended semiclassical analysis, we explore in-depth the roles of various quantum trajectories, including short- and long trajectories, multiphoton trajectories, resonance-enhanced trajectories, and multiple rescattering trajectories of the below- and near- threshold harmonic generation processes. Our results shed new light on the dynamicalorigin of the below- and near-threshold harmonic generation and various quantum trajectories for diatomic molecules for the first time.

No MeSH data available.