Quantum Trajectory Selector: Attosecond Study of Strong Field Ionization

The dynamics of an electron photoionized by an intense laser field is commonly understood using the semi-classical model: the electron first tunnels out of the atomic potential, then is accelerated in the strong field, and finally recollides with its parent ion. One constraint of studying strong field processes is that tunneling can occur at times within the strong field cycle that are weighted by the instantaneous ionization probability proportional to the field strength, thus only a limited phase space of all possible trajectories contributes to the measurement. We introduce the quantum trajectory selector (QTS) method capable of decoupling ionization from acceleration and recollision using an extreme ultraviolet (XUV) attosecond pulse train to ionize the target dressed by a strong near-infrared (NIR) pulse that accelerates the electron and drives recollision. A variable delay between the XUV and NIR pulses enables control of the electron's release time in the strong field, accessing a well-defined set of trajectories. Here, we apply the QTS method to study non-sequential double ionization in argon. Our work shows the promise of the QTS method for studying strong field processes and providing control of strong field phenomena with unprecedented breadth and sensitivity.