Efficient and robust coherent electronic excitation in molecules with temporally shaped femtosecond laser pulses

点击翻译按钮获取中文摘要

Coherent electronic excitation in atoms with the help of laser light forms the basis of many quantum technologies. Adiabatic processes are of particular interest, as they allow for efficient population transfer (up to 100%) and in addition show robustness with respect to variations of experimental parameters as for example intensity fluctuations. Rapid Adiabatic Passage (RAP) is a prime example to that end. Nuclear motion in molecules hampers such excitation processes significantly. Therefore adiabatic excitation in molecules is neither theoretically nor experimentally thoroughly explored. More than a decade ago theory proposed excitation with ultra broadband short laser pulses being stretched via a linear frequency sweep into the picosecond regime. In this limit the excitation is similar to the atomic RAP case, experimental realizations were not reported. We now suggest to adapt the electric field of a laser well directed to the coupled electron nuclear dynamics via specific frequency sweeps and temporal intensity envelopes in order to demonstrate robust population transfer in a molecule. Simulations on a simple harmonic oscillator model reveal efficient and robust new excitation schemes. Taking the potassium dimer as a prototype, this project aims at experimental demonstrations of these excitation schemes. Specifically shaped laser pulses are used for excitation and the final population in the neutral manifold is probed via photoelectron spectroscopy with the help of a temporally delayed laser pulse. It is beneficial to use the potassium dimer as a prototype as quantum mechanical simulations can be performed with high accuracy on this molecule. The joint expertise of the Baumert group (Uni Kassel; experiment) and Wollenhaupt group (Uni Oldenburg; quantum mechanical simulations) is brought together in order to explore the limits of such an approach by a direct comparison of experiments on this molecule to simulations.