Correlated electron-nuclear dynamics in above-threshold multiphoton ionization of asymmetric molecule

Strong-field double ionization dynamics of vibrating HeH+ versus HeT. OPTICS EXPRESS 2020;28:4650-4660. [PMID: 32121698 DOI: 10.1364/oe.384242] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

We study double ionization (DI) dynamics of vibrating HeH⁺ versus its isotopic variant HeT⁺ in strong laser fields numerically. Our simulations show that for both cases, these two electrons in DI prefer to release together along the H(T) side. At the same time, however, the single ionization (SI) is preferred when the first electron escapes along the He side. This potential mechanism is attributed to the interplay of the rescattering of the first electron and the Coulomb induced large ionization time lag. On the other hand, the nuclear motion increases the contributions of these two electrons releasing together along the He side. This effect differentiates DI of HeH⁺ from HeT⁺.

Heteronuclear Limit of Strong-Field Ionization: Fragmentation of HeH^{+} by Intense Ultrashort Laser Pulses

The laser-induced fragmentation dynamics of this most fundamental polar molecule HeH^{+} are measured using an ion beam of helium hydride and an isotopologue at various wavelengths and intensities. In contrast to the prevailing interpretation of strong-field fragmentation, in which stretching of the molecule results primarily from laser-induced electronic excitation, experiment and theory for nonionizing dissociation, single ionization, and double ionization both show that the direct vibrational excitation plays the decisive role here. We are able to reconstruct fragmentation pathways and determine the times at which each ionization step occurs as well as the bond length evolution before the electron removal. The dynamics of this extremely asymmetric molecule contrast the well-known symmetric systems leading to a more general picture of strong-field molecular dynamics and facilitating interpolation to systems between the two extreme cases.

Correlated electron dynamics in strong-field nonsequential double ionization of Mg

Using the classical ensemble model, we systematically investigate strong-field nonsequential double ionization (NSDI) of Mg by intense elliptically polarized laser pulses with different wavelengths. Different from the noble atoms, NSDI occurs for Mg driven by elliptically and circularly polarized laser fields. Our results show that in elliptically and circularly polarized laser fields, the NSDI yield is sharply suppressed as the wavelength increases. Interestingly, the correlated behavior in the electron momentum spectra depends sensitively on the wavelengths. The corresponding electron dynamics is revealed by back tracing the classical trajectory.

Carrier-envelope phase dependent photoelectron energy spectra in low intensity regime

We study the carrier-envelope phase (CEP) dependent photoelectron energy spectra from above-threshold ionization by numerically solving the time-dependent Schrödinger equation of hydrogen atom in a few-cycle laser field at intensities in the range of (2-10) × 10¹³ W/cm². Depending on the electron energy and the laser intensity, the yield of the photoelectron reveals clear oscillations with respect to the CEP. At high laser intensities (larger than ~3 × 10¹³ W/cm²), the yield of the high-energy photoelectrons (larger than 2U_p, with U_p being the ponderomotive potential) shows two kinds of oscillations with the CEP for different electron energies. There is a clear phase jump for those two kinds of oscillations. In contrast, at low laser intensities (smaller than ~3 × 10¹³ W/cm²), the phase of the oscillation for the high-energy photoelectron yield with the CEP is nearly independent on the electron energy, which will reduce the sensitivity of the retrieval of single-shot CEP using the method reported by T. Wittmann et al. [Nat. Phys. 5, 357 (2009)] at low laser intensities. We further show that the low-energy photoelectrons display distinct CEP-dependent intercycle interference fringes, providing an alternative approach to retrieve the CEP with high sensitivity in a few-cycle laser field with low intensity.

Dissection of electron correlation in strong-field sequential double ionization using a classical model

Recent experiments on strong-field sequential double ionization (SDI) have reported several observations which are regarded as evidence of electron correlation, querying the validity of the standard independent electron approximation for SDI. Here we theoretically study SDI with a classical ensemble model. The experimental results are well reproduced with this model. Back tracing of the ionization process shows that these results are ascribed to the subcycle ionization dynamics of the two electrons, not the evidences of the electron correlation in SDI. Thus, the previously reported observations are not enough to claim the breakdown of the independent electron approximation in SDI.