Identifying spatially asymmetric high-order harmonic emission in the falling edge of an intense laser pulse

Vafaee, Mohsen; Ahmadi, Hamed

doi:10.1088/1361-6455/50/2/025601

Cited by 13 publications

(5 citation statements)

References 31 publications

(44 reference statements)

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“…) is a Hanning window function [42] that smoothly brings the time-dependent acceleration to zero at the end of the time integration. As has been discussed previously [23,43,44], it is necessary to include a window function on a(t) in numerical calculations to act as an artificial lifetime on the excited states by ending any coherence between the ground state and population left in the excited states at the end of a calculation. For most of this paper, τ H is chosen to bring the window function to 0 at the end of the laser pulse, allowing us to consider only the coherent, driven response of the atom to the laser pulse.…”

Section: Theoretical Methodsmentioning

confidence: 99%

Resonantly-initiated quantum trajectories and their role in the generation of near-threshold harmonics

Camp¹,

Beaulieu²,

Schafer³

et al. 2018

J. Phys. B: At. Mol. Opt. Phys.

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We present a theoretical study of the role that resonant enhancement plays in the temporal and spectral properties of near-threshold harmonics in argon, driven by a moderately intense, nearinfrared laser pulse. By studying how the temporal profile of the eleventh harmonic (H11) changes with peak intensity and pulse duration, we show that H11 is predominantly emitted when the instantaneous intensity of the laser pulse is such that a high-lying excited state is Stark-shifted into multiphoton resonance with the ground state. We demonstrate that if this resonant intensity is lower than the peak intensity, the harmonic pulse will in general exhibit two peaks in time, on the rising and falling edges of the laser pulse. The resonantly enhanced harmonic radiation exhibits strong characteristics of semi-classical long and short quantum paths, and in general both paths are enhanced by the resonance. We find that the resonant enhancement leads to the harmonic radiation being emitted between .5 and 1.1 optical cycles after the time of multiphoton resonance, indicating that the resonance introduces a delay as compared to non-resonant emission. We further demonstrate that the resonantly enhanced long-trajectory contribution to the harmonic radiation manifests in the spectral domain as red-and blueshifted features near the central harmonic frequency. Finally, we compare the single argon atom response to the macroscopic response of an argon gas and show that spectral and temporal effects of the resonance are still recognizable after propagation.

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Section: Theoretical Methodsmentioning

confidence: 99%

Resonantly-initiated quantum trajectories and their role in the generation of near-threshold harmonics

Camp¹,

Beaulieu²,

Schafer³

et al. 2018

J. Phys. B: At. Mol. Opt. Phys.

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“…Furthermore, redshift in HHG is commonly expected for any molecule beyond the Born-Oppenheimer approximation [17,18]. In recent years, great effort has been made to probe the effect of nuclear dynamics on high harmonic spectroscopy [19][20][21].…”

Section: = +mentioning

confidence: 99%

Role of nuclear dynamics in high harmonic generation redshift of H₂ ⁺

Taghipour,

Vafaee,

Ahmadi

2023

Phys. Scr.

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The detailed spectral and temporal structures of high-order harmonic generation (HHG) have provided us with a wealth of information about the highly nonlinear response of atoms, molecules, and electronic structures to intense low-frequency laser fields. In this study, we aim to investigate the underlying physics behind the molecular high harmonic spectra redshift beyond the Born Oppenheimer approximation for H2+ and its isotopes with numerical simulations of the time-dependent Schrödinger equation. One widely recognized phenomenon is the occurrence of a spectral redshift at the trailing edge of a laser pulse. However, our findings reveal that even when driven by a sinusoidal laser pulse without a falling edge, the HHG redshift appears and highlights that the observed spectral redshift is not solely due to the declining intensity of the laser pulse. We show that it is a direct consequence of the decrease in ionization energy during the transition from recombination time to ionization time within wave packets at short internuclear distances. Interestingly, our results also demonstrate how a sinusoidal laser pulse without a rising part can disrupt the standard picture of redshift in literatures in the past. This finding suggests that there are additional factors influencing the redshift mechanism beyond just the trailing edge of the laser pulse. These phenomena are elucidated through the analysis of the dynamics of the nuclear wave packet. Our study provides valuable insights into the complex dynamics of HHG processes and sheds light on how different laser pulse characteristics can influence spectral redshifts and harmonic generation in molecular systems.

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“…This approach is implementable for simulating systems with a limited number of particles in a limited region of momentum or coordinate space. There are different TDSE approaches for simulating the electron dynamics in an atomic or molecular laser-induced system in one, two, or three (full) coordinate (or momentum) dimensions [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Some of the TDSE approaches treat the nuclei in the laser-induced system dynamically using classical or quantum mechanics.…”

Section: Introductionmentioning

confidence: 99%

Static Coherent States Method: One- and Two-Electron Laser-Induced Systems with Classical Nuclear Dynamics

2018

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Featured Application: We present a new computational method that can be used to investigate the quantum dynamics of one-or two-electron systems during interaction with an ultrashort laser pulse, including nuclear dynamics. The inclusion of both electronic and nuclear degrees of freedom allows for a description of a wide range of processes, including charge migration during the nuclear dissociation process. Abstract:In this report, we introduce the static coherent states (SCS) method for investigating quantum electron dynamics in a one-or two-electron laser-induced system. The SCS method solves the time-dependent Schrödinger equation (TDSE) both in imaginary and real times on the basis of a static grid of coherent states (CSs). Moreover, we consider classical dynamics for the nuclei by solving their Newtonian equations of motion. By implementing classical nuclear dynamics, we compute the electronic-state potential energy curves of H + 2 in the absence and presence of an ultra-short intense laser field. We used this method to investigate charge migration in H + 2 . In particular, we found that the charge migration time increased exponentially with inter-nuclear distance. We also observed substantial charge localization for sufficiently long molecular bonds.

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Identifying spatially asymmetric high-order harmonic emission in the falling edge of an intense laser pulse

Cited by 13 publications

References 31 publications

Resonantly-initiated quantum trajectories and their role in the generation of near-threshold harmonics

Resonantly-initiated quantum trajectories and their role in the generation of near-threshold harmonics

Role of nuclear dynamics in high harmonic generation redshift of H₂ ⁺

Static Coherent States Method: One- and Two-Electron Laser-Induced Systems with Classical Nuclear Dynamics

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Identifying spatially asymmetric high-order harmonic emission in the falling edge of an intense laser pulse

Cited by 13 publications

References 31 publications

Resonantly-initiated quantum trajectories and their role in the generation of near-threshold harmonics

Resonantly-initiated quantum trajectories and their role in the generation of near-threshold harmonics

Role of nuclear dynamics in high harmonic generation redshift of H2 +

Static Coherent States Method: One- and Two-Electron Laser-Induced Systems with Classical Nuclear Dynamics

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Product

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Role of nuclear dynamics in high harmonic generation redshift of H₂ ⁺