Abstract
1 Introduction
Both electronic and nuclear vibrational dynamics play a crucial role in molecular reactions, such as molecular ionization, dissociation and isomerization[
Four types of strong-field-induced EWP interferences in molecules can be distinguished: the first type is the inter-cycle interference (ICI) produced by EWPs released during different optical cycles which lead to above-threshold ionization (ATI)-like structures in the momentum or the energy distribution of photoelectrons[
To obtain a well-defined interference pattern of EWPs, a cycle-shaped laser field is beneficial, because the EWP interference patterns are induced by EWPs released at different times. Their release times are thus extremely sensitive to the shape of the laser field and can be controlled by the shape of the cycle of the laser field. There are several ways to obtain such laser fields. One of the most straightforward methods is to stabilize the carrier-envelope phase of a few-cycle laser pulse. Another method is to lock the phase delay between multiple laser fields with different colors. Such cycle-shaped laser fields have been applied to controlling high harmonic generation[
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In this work, we employed a two-color laser field with precise control over the relative phase between a fundamental laser field and its second harmonic. In a previous study[
In the case of molecules, because of the small differences in the ionization potentials and the different angular dependence of ionization rates for different orbitals, tunnel ionization may happen from lower lying molecular orbitals rather than only from the HOMO[
A schematic view of subcycle EWP interference is shown in Figure
2 Experiments
Coincidence measurements of electrons and ions were performed for
3 Results and discussion
3.1
When a hydrogen molecule interacts with a strong laser field, one electron can be removed through tunnel ionization. After single ionization, the molecule will reach a cationic state.
First we focus on the channel leading to
3.2 Photoelectron momentum distribution over relative phase
Measured distributions of the
3.3 Subcycle interferences of electron wave packets correlated with
To observe SCI structures we investigate electron momentum distributions for certain relative phases between the two colors, since for electrons the momentum resolution is much higher than that for ions along the directions perpendicular to the laser polarization direction. The measured electron momentum distributions in the laser polarization plane are illustrated in Figures
First, we focus on the results with relative phase 0. According to the shape of the vector potential [Figure
For a relative phase of
When the relative phase between the two colors varies, the shape of the laser field’s cycle varies. Since tunneling ionization is very sensitive to the field strength of a laser field, the ionization time within an optical cycle depends delicately on the shape of the laser cycle. As a result, SCI structures can be sensitively controlled by varying the relative phase of the two-color field. As shown in Figure
3.4 Subcycle interferences of electron wave packets for dissociation channels
After single ionization in a two-color field,
In Figure
4 Conclusion
In conclusion, we demonstrated a proof-of-principle experiment of channel-resolved interferometry based on SCI of EWPs released during strong field interaction of
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