Coherent strong-field control of multiple states by a single chirped femtosecond laser pulse

Abstract

We present a joint experimental and theoretical study on strong-field photo-ionization of sodium atoms using chirped femtosecond laser pulses. By tuning the chirp parameter, selectivity among the population in the highly excited states 5p, 6p, 7p and 5f , 6f is achieved. Different excitation pathways enabling control are identified by simultaneous ionization and measurement of photoelectron angular distributions employing the velocity map imaging technique. Free electron wave packets at an energy of around 1 eV are observed. These photoelectrons originate from two channels. The predominant 2+1+1 Resonance Enhanced Multi-Photon Ionization (REMPI) proceeds via the strongly driven two-photon transition 4s ←← 3s, and subsequent ionization from the states 5p, 6p and 7p whereas the second pathway involves 3+1 REMPI via the states 5f and 6f . In addition, electron wave packets from two-photon ionization of the non-resonant transiently populated state 3p are observed close to the ionization threshold. A mainly qualitative five-state model for the predominant excitation channel is studied theoretically to provide insights into the physical mechanisms at play. Our analysis shows that by tuning the chirp parameter the dynamics is effectively controlled by dynamic Stark-shifts and level crossings. In particular, we show that under the experimental conditions the passage through an uncommon three-state "bow-tie" level crossing allows the preparation of coherent superposition states.

Adaptive strong-field control of chemical dynamics guided by three-dimensional momentum imaging

“…Although past work has combined strong field pulse shaping with imaging [23][24][25] , and a few previous efforts [26][27][28][29] used VMI for adaptive control, they were exclusively based on raw images, in which the 3D momentum distributions were projected onto the two-dimensional (2D) detector plane. The azimuthal ambiguity inherent in such raw, 2D images complicated the extraction of a robust feedback signal 26 .…”

Incorporating real time velocity map image reconstruction into closed-loop coherent control

“…In fact, imaging studies of pulse-shape-dependent strong-field processes have appeared, [18][19][20][21] and some initial image-based feedback techniques have already been used by various groups. [21][22][23][24] In these initial efforts, the raw two-dimensional (2D) image was used as feedback.…”

Numerical investigation of the sequential-double-ionization dynamics of helium in different few-cycle-laser-field shapes

“…Chirped pulses are a well-established tool in molecular and atomic quantum control with femtosecond pulses [11][12][13][14][15]. In contrast, the influence of chirp is rarely considered for extremely fast processes such as strong-field tunnel ionization on the attosecond time scale.…”