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We present a pulse-shaper-based holographic technique for the time-resolved and phase-sensitive observation of ultrafast quantum dynamics. The technique combines bichromatic white light polarization pulse shaping with the tomographic reconstruction of photoelectron wave packets. The physical scheme is based on the interference of a probe wave packet from $N+1$ resonance-enhanced multiphoton ionization via the target states and a reference wave packet from $M+1$ multiphoton ionization of the ground state. To create the wave packets, we employ carrier-envelope phase stable bichromatic ($M\ensuremath{\omega}$:$N\ensuremath{\omega}$) pump-probe pulse sequences. The scheme is demonstrated on femtosecond Rydberg wave-packet dynamics in potassium atoms using corotating circularly polarized ($2\ensuremath{\omega}$:$3\ensuremath{\omega}$) pulse sequences. The interference of continuum states with different angular momenta yields a crescent-shaped photoelectron wave packet rotating in the laser polarization plane due to the interplay of the optical phase and the accumulated quantum phase. Carrier-envelope phase control of the rotation provides access to the photoelectron asymmetry, enabling background-free detection of the crescent's angular motion which maps the bound-electron dynamics.

We report on recent developments in coherent control of ultrafast photoionization dynamics with ultrashort polarization-shaped bichromatic pulse sequences. In the experiments, a novel pulse shaping scheme for the generation of Bichromatic Carrier-Envelope phase-stable Polarization-tailored Supercontinuum (BiCEPS) fields is combined with high-resolution photoelectron tomography to create, manipulate and reconstruct three-dimensional free electron wave packets from atomic multiphoton ionization. Examples for coherent control with bichromatic polarization-shaped pulse sequences are presented, including the generation of unusual angular momentum superposition states, carrier-envelope phase control of directional photoemission, the creation and manipulation of photoelectron vortices and electron wave packets with odd-numbered rotational symmetry as well as studies on ultrafast Rydberg and spin-orbit wave packet dynamics.

We present a novel concept for the generation of ultrashort polarization-shaped bichromatic laser fields. The scheme utilizes a 4f polarization pulse shaper based on a liquid crystal spatial light ...

Polarization-tailored bichromatic femtosecond laser fields with cycloidal polarization profiles have emerged as a powerful tool for coherent control of quantum processes. We present an optical scheme to create and manipulate three-dimensional free electron wave packets with arbitrary rotational symmetry by combining advanced supercontinuum pulse shaping with high resolution photoelectron tomography. Here we use carrier-envelope phase-stable polarization-tailored bichromatic (3ω:4ω) counter- and corotating femtosecond laser pulses to generate 7-fold rotational symmetric and asymmetric photoelectron momentum distributions by multiphoton ionization of sodium atoms. To elucidate the physical mechanisms, we investigate the interplay between the symmetry properties of the driving field and the resulting electron wave packets by varying the optical field parameters. Our results show that the symmetry properties of electron wave packets are not fully determined by the field symmetry, but completely described by multipath quantum interference of states with different angular momenta., Laser fields can be tuned to probe electronic motion in atoms and molecules. Here the authors ionize Na atoms using bichromatic pulses to generate electron wave packets of crescent-shaped and 7-fold rotational symmetry which do not follow the field symmetry but are determined by multiphoton interference.

We combine a bichromatic white light polarization pulse shaping scheme with angle- and energy-resolved photoelectron spectroscopy to image the dynamics of atomic Rydberg wave packets. Background-free detection of the Rydberg dynamics is performed using shaper-generated bichromatic linearly and circularly polarized femtosecond pump-probe pulse sequences. Photoelectron momentum distributions from linearly polarized bichromatic fields feature pronounced time-, energy-, and angle-dependent dynamics, which result from the interference of $s$-, $d$-, and $g$-type photoelectron wave packets from the ionization of the Rydberg $np$ and $nf$ series. Detailed analysis of the highly differential data allows us to extract the dynamics of both Rydberg wave packets separately. The results are experimentally verified by additional pump-probe studies with bichromatic circularly polarized pulse sequences, which exclusively map the dynamics of the Rydberg $nf$ series via $g$-type photoelectron wave packets.

Synopsis Using a 4f pulse shaper in combination with a Reaction Microscope we performed 800 nm pump-probe experiments with orthogonally polarized pulses on H₂.

We report on the creation and manipulation of three-dimensional (3D) electron vortices from femtosecond multiphoton ionization of atoms. Vortex-shaped photoelectron momentum distributions arise from the superposition of two time-delayed free-electron wave packets with different magnetic quantum numbers. In the experiment, pairs of time-delayed counter-rotating circularly polarized (CRCP) femtosecond laser pulses, generated from a polarization-shaped supercontinuum source, are used to ionize potassium atoms. The resulting 3D electron vortices are reconstructed tomographically from a set of velocity map imaging measurements. By variation of the time delay, the helicity, and the spectral bandwidth of the CRCP pulse sequence, we control the radial vortex shape. Absorption of another photon in the continuum changes the ${c}_{6}$ azimuthal symmetry of the threshold vortex into ${c}_{8}$ for above-threshold ionization. Electron vortices from nonperturbative excitation show ${c}_{4}$ azimuthal symmetry and a $\ensuremath{\pi}$-phase jump in the polar direction. Determination of the relative phase of the superposition state allows us to reconstruct a free-electron wave function.

Multiphoton ionization of potassium atoms with a sequence of two counter-rotating circularly polarized femtosecond laser pulses produces vortex-shaped photoelectron momentum distributions in the polarization plane describing Archimedean spirals. The pulse sequences are produced by polarization shaping and the three-dimensional photoelectron distributions are tomographically reconstructed from velocity map imaging measurements. We show that perturbative ionization leads to electron vortices with c_{6} rotational symmetry. A change from c_{6} to c_{4} rotational symmetry of the vortices is demonstrated for nonperturbative interaction.

We demonstrate CEP control of the directional photoemission from multiphoton ionization (MPI) of xenon atoms using (7ω:8ω) bichromatic fields whose frequency ratio is tailored to the order of the MPI process. The bichromatic fields are generated by white light supercontinuum polarization pulse shaping. In the experiment, we observe a CEP-sensitive lateral asymmetry of up to 70%. The CEP sensitivity arises from interference of opposite parity continuum states coupled to the ground state by a different number of photons.

Kurzlich ist es gelungen, die Wechselwirkung ultrakurzer, polarisationsgeformter Laserpulse mit Atomen derart zu kontrollieren, dass bei der Photoionisation Elektronenwirbel entstehen[1]. Elektronenwirbel sind faszinierende quantenmechanische Uberlagerungszustande, die durch Interferenz zweier entgegengesetzt rotierender, freier Elektronenwellenpakete entstehen.