68
S. Kerbstadt et al.
Fig. 3.13 Time-resolved imaging of ultrafast SOWP dynamics in the K 4 p fine structure doublet
using shaper-generated bichromatic OLP pump-probe pulse sequences. The corresponding excitation and ionization scheme is depicted in (a). The resonant p-polarized blue pulse (pump) excites the
states 4 p 1/2 and 4 p 3/2 and launches a bound SOWP with an oscillation period of T = 580 fs. After
a variable time τ the SOWP is probed via non-resonant two-photon ionization by the s-polarized
red pulse, mapping the bound state dynamics into the ε 1 -channel for background-free detection.
For τ = 0, we measure a PMD with quasi c 6 rotational symmetry aligned in the laser polarization
plane (see discussion in Sect. 3.3.1; cf. Fig. 3.5c). b Around half period τ ≈ T /2 the reconstructed
PMD rotates by 90 ◦ about the x-axis into an alignment coplanar to the laser propagation direction.
This rotation indicates the orbital realignment of the SOWP from a dumbbell oriented along the
pump polarization (y-axis) into a torus aligned in the x-z-plane (see simulation in bottom insets). c
After a full cycle τ = T the measured PMD recovers the initial shape, indicating the return of the
SOWP to its dumbbell-shaped spatial distribution
Recently, the incommensurable frequency mixing scheme described in Sect. 3.3.1
was applied in a two-color pump-probe experiment for 3D spatial imaging of ultrafast SOWP dynamics in the K 4 p fine structure doublet [51]. The corresponding
(1+2) REMPI scheme is depicted in Fig. 3.13a. In this experiment, the p-polarized
blue pulse serves as a pump to resonantly excite the SOWP composed of the states
4 p 1/2 and 4 p 3/2 . The corresponding oscillation period T = 580 fs, derived from the
energy splitting of = 7 meV, is much larger than the pulse duration = 80 fs
of both colors. After a variable time delay τ , introduced by linear spectral phase
modulation, the SOWP is probed by the s-polarized red pulse via non-resonant twophoton ionization. The probe maps the time evolution of the SOWP exclusively into
the ε 1 -channel, thus disentangling photoelectron contributions carrying dynamical
information from the τ -insensitive single-color contributions at ε 0 and ε 3 . By this
means, the bichromatic approach provides background-free detection of the bound
state dynamics imaged into the 3D PMD of the ε 1 -channel. Tomographic reconstruction of the created photoelectron wave packet as a function of time reveals the orbital
realignment dynamics of the SOWP in the neutral system.
S. Kerbstadt et al.
Fig. 3.13 Time-resolved imaging of ultrafast SOWP dynamics in the K 4 p fine structure doublet
using shaper-generated bichromatic OLP pump-probe pulse sequences. The corresponding excitation and ionization scheme is depicted in (a). The resonant p-polarized blue pulse (pump) excites the
states 4 p 1/2 and 4 p 3/2 and launches a bound SOWP with an oscillation period of T = 580 fs. After
a variable time τ the SOWP is probed via non-resonant two-photon ionization by the s-polarized
red pulse, mapping the bound state dynamics into the ε 1 -channel for background-free detection.
For τ = 0, we measure a PMD with quasi c 6 rotational symmetry aligned in the laser polarization
plane (see discussion in Sect. 3.3.1; cf. Fig. 3.5c). b Around half period τ ≈ T /2 the reconstructed
PMD rotates by 90 ◦ about the x-axis into an alignment coplanar to the laser propagation direction.
This rotation indicates the orbital realignment of the SOWP from a dumbbell oriented along the
pump polarization (y-axis) into a torus aligned in the x-z-plane (see simulation in bottom insets). c
After a full cycle τ = T the measured PMD recovers the initial shape, indicating the return of the
SOWP to its dumbbell-shaped spatial distribution
Recently, the incommensurable frequency mixing scheme described in Sect. 3.3.1
was applied in a two-color pump-probe experiment for 3D spatial imaging of ultrafast SOWP dynamics in the K 4 p fine structure doublet [51]. The corresponding
(1+2) REMPI scheme is depicted in Fig. 3.13a. In this experiment, the p-polarized
blue pulse serves as a pump to resonantly excite the SOWP composed of the states
4 p 1/2 and 4 p 3/2 . The corresponding oscillation period T = 580 fs, derived from the
energy splitting of = 7 meV, is much larger than the pulse duration = 80 fs
of both colors. After a variable time delay τ , introduced by linear spectral phase
modulation, the SOWP is probed by the s-polarized red pulse via non-resonant twophoton ionization. The probe maps the time evolution of the SOWP exclusively into
the ε 1 -channel, thus disentangling photoelectron contributions carrying dynamical
information from the τ -insensitive single-color contributions at ε 0 and ε 3 . By this
means, the bichromatic approach provides background-free detection of the bound
state dynamics imaged into the 3D PMD of the ε 1 -channel. Tomographic reconstruction of the created photoelectron wave packet as a function of time reveals the orbital
realignment dynamics of the SOWP in the neutral system.