Probing and Controlling Electron Dynamics at the Attosecond Timescale

Abstract

A recently established attosecond beamline, for studies controlling and probing electron dynamics, has been stabilized with attosecond precision. The design and performance of the active stabilization system is presented. The system uses a continuous wave (CW) laser which is propagated coaxially with the beams in the interferometer. The stabilization is achieved with a standalone feedback controller that adjusts the length of one of its arms to maintain a constant relative phase between the CW beams. The time delay between the pump and probe beams is stabilized within 10 as rms. Coherent control of photoemission in atoms was performed via attosecond pulseshaping. The photoelectron emission from argon gas was produced by absorption of an attosecond pulse train (APT) made of extreme ultraviolet odd and even harmonics. The photoemission can be manipulated along the direction of polarization of the light by tuning the spectral amplitude and phase of the pulse. In addition, the APTs produced with a two-color (400-nm plus 800-nm) femtosecond driving field exhibit high temporal tunability, which is optimized for an intensity ratio between the two colors in the range of 0.1% to 5%. A methodology is demonstrated for isolating the continuum-continuum delays of an atomic target during laser-assisted photoionization. Argon gas is ionized by an APT, and dressed by a probe-pulse in configurations like those reported for the Reconstruction of Attosecond Harmonic Beating by Interference of Two-photon Transitions (RABBITT) technique. Complementary measurements are performed that allow the continuum-continuum delays to be obtained across excitations from 23 eV to 30 eV. These delays are compared to calculations based on the asymptotic approximation of transition matrix elements.