"Attoclock-Rabbitt" - Bicircular laser fields as tool for molecular ionization time measurements

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This project aims to exploit tailored light fields as a tool to answer a seemingly simple question: Does the emission time of a photoelectron ejected from a molecule by multiphoton absorption depend on its emission direction? To give an example: we ask whether the ejection of an electron from CO takes longer in case of emission towards the C or towards the O side of the molecule. The expected time differences are in the attosecond regime. Quantum mechanically time-differences are encoded in phase-differences, thus our question translates to determining the phase of the electron wave packet as function of angle to the molecular axis. To measure this phase, we suggest a new scheme termed “Attoclock-RABBITT”. Within this scheme, we combine the measurement of an ionization instant (in a manner similar to the established RABBITT technique) with a COLTRIMS Reaction Microscope, which gives access to the molecular frame of reference by detection the molecular ion fragments.The employed laser field will consist of a strong circularly polarized 400 nm field mixed with a weak circular 800nm co-rotating dressing field. As we have learned in the previous QUTIF funding period, this bicircular field combination maps the relative phase between the two colors to an electron emission angle in the laboratory frame. Sidebands in the electron ATI spectrum show the known RABBITT intensity oscillations as function of that angle and from these oscillations, one can deduce the emission times. In our suggested approach, the emitted electrons are measured in coincidence with ionic fragments of the molecule using a COLTRIMS Reaction Microscope. From the emission direction of the ionic fragments we are able to deduce the molecular orientation. This way we obtain the “Attoclock-RABBITT” traces, i.e. ionization times, in the molecular frame. As this is a novel scheme, we suggest to first benchmarking it on atomic hydrogen. We will then use it to study the following predicted effects: Using Ne2 we will search for the predicted divergence of the ionization time at a Cohen/Fano-interference. Employing H2 we will provide benchmark data on the only molecule for which quasi-exact theoretical treatment is possible today. In experiments on CO we will search for the predicted asymmetries of the emission time to the two sides and, aim to visualize a shape resonance in the time domain. Finally, for CF4 we will test if the technique can be applied to more complex molecules. The project is at the heart of QUTIF as the types of tailored field have been explored in several previous QUTIF projects. The first funding period has led to widespread theoretical experience in handling these fields. Also experimentally, the optical tools for this project have been developed. Without this extensive experience from QUTIF it would not have been possible to now aim for the next step of application of tailored fields.