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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.


Related in: MedlinePlus

Semiclassical trajectories: Position and time, and scheme of resonance and continuum electron dynamics.(a) Several trajectories in below-threshold HHG (resonant). The red and blue squares are the corresponding time of release for the electron from either the right (blue) or left (red) hydrogen core. (b) Several trajectories in above-threshold HHG (continuum). Here the initial condition is that the electrons with an initial velocity v0 are released ‘opposite’ to the electronic-field force Fz from the left and right hydrogen cores (z = ±1 a.u.). The green solid line indicates the corresponding laser field, and the laser parameters used are the same as those in Fig. 1.
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f4: Semiclassical trajectories: Position and time, and scheme of resonance and continuum electron dynamics.(a) Several trajectories in below-threshold HHG (resonant). The red and blue squares are the corresponding time of release for the electron from either the right (blue) or left (red) hydrogen core. (b) Several trajectories in above-threshold HHG (continuum). Here the initial condition is that the electrons with an initial velocity v0 are released ‘opposite’ to the electronic-field force Fz from the left and right hydrogen cores (z = ±1 a.u.). The green solid line indicates the corresponding laser field, and the laser parameters used are the same as those in Fig. 1.

Mentions: To explain the detailed electronic dynamic behaviors in the below-, near-, and above-threshold harmonic generation, the positions (z) of the electrons as a function of time are shown in Figs 3c and 4a,b, respectively. Figure 3c shows the position of the electrons as a function of the time in the below-, near- and above-threshold regions; the corresponding initial condition is marked by the arrows in Fig. 3b. Initially the electrons with a small velocity are released along (or against) the laser field direction at either hydrogen cores (z = ±1 a.u.); here the minimum initial velocity is v0 = 0 and the maximum is the height of the barrier at the time of release, and typically the initial velocities used are/v0/ ≤ 1.0 (in a.u.). Figure 3c presents several short trajectories (first return), long trajectories (first return), and multi-rescattering trajectories (second through third return) in below-, near- and above-threshold HHG along with the corresponding laser field.


Unravelling the dynamical origin of below- and near-threshold harmonic generation of H 2 + in an intense NIR laser field
Semiclassical trajectories: Position and time, and scheme of resonance and continuum electron dynamics.(a) Several trajectories in below-threshold HHG (resonant). The red and blue squares are the corresponding time of release for the electron from either the right (blue) or left (red) hydrogen core. (b) Several trajectories in above-threshold HHG (continuum). Here the initial condition is that the electrons with an initial velocity v0 are released ‘opposite’ to the electronic-field force Fz from the left and right hydrogen cores (z = ±1 a.u.). The green solid line indicates the corresponding laser field, and 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

f4: Semiclassical trajectories: Position and time, and scheme of resonance and continuum electron dynamics.(a) Several trajectories in below-threshold HHG (resonant). The red and blue squares are the corresponding time of release for the electron from either the right (blue) or left (red) hydrogen core. (b) Several trajectories in above-threshold HHG (continuum). Here the initial condition is that the electrons with an initial velocity v0 are released ‘opposite’ to the electronic-field force Fz from the left and right hydrogen cores (z = ±1 a.u.). The green solid line indicates the corresponding laser field, and the laser parameters used are the same as those in Fig. 1.
Mentions: To explain the detailed electronic dynamic behaviors in the below-, near-, and above-threshold harmonic generation, the positions (z) of the electrons as a function of time are shown in Figs 3c and 4a,b, respectively. Figure 3c shows the position of the electrons as a function of the time in the below-, near- and above-threshold regions; the corresponding initial condition is marked by the arrows in Fig. 3b. Initially the electrons with a small velocity are released along (or against) the laser field direction at either hydrogen cores (z = ±1 a.u.); here the minimum initial velocity is v0 = 0 and the maximum is the height of the barrier at the time of release, and typically the initial velocities used are/v0/ ≤ 1.0 (in a.u.). Figure 3c presents several short trajectories (first return), long trajectories (first return), and multi-rescattering trajectories (second through third return) in below-, near- and above-threshold HHG along with the corresponding 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.


Related in: MedlinePlus