Multiphoton ionization with three-dimensional light fields

Abstract

We report the first observation of free-electron angular momentum wave packets generated by atomic multiphoton ionization with bichromatic three-dimensional (3D) polarization-tailored ultrashort laser fields. These fields, created by the non-collinear superposition of two polarization-shaped pulses of different colors from a supercontinuum polarization pulse shaper, provide electric-field components along all spatial directions. The resulting photoelectron momentum distributions, recorded via velocity map imaging, demonstrate full 3D coherent control of electronic superposition states extending beyond the constraints of planar polarization fields by unlocking all dipole selection rules $Δm = 0,\pm1$. As an application, 3D pump-probe fields are used to image previously unobserved photoelectron wave packets mapping spin-orbit dynamics of the potassium $3d$ fine structure doublet. Our shaper-based approach establishes a route to fully controllable 3D light fields for chiral-sensitive light-matter interactions and ultrafast spectroscopy.

Figures (4)

• Figure 1: (a) Simplified (left) and detailed (right) bichromatic excitation scheme for the potassium atom interacting with a 3D laser field. (b) Schematic of the experimental setup including the pulse shaper, the non-collinear interferometer and the VMI spectrometer. (c) Illustration of the experiment.
• Figure 2: (a) Measured optical spectra. (b) VMI images recorded in spatial imaging mode for the colors individually and combined. VMI images recorded in momentum imaging mode for the (c) PLP and (d) COCP configuration for blue pulse (left), red pulse (center) and both pulses combined (right). The two-color signal created by the 3D fields is indicated by purple circles marking the ROI.
• Figure 3: First row: 3D fields for the PLP, COCP, CRCP, RLBC and RCBL configuration. Second row: Measured VMI images within the ROI. Third and forth row: Simulated 2D projections and 3D densities of the PMDs. The insets show the decomposition of the wave packets into angular momentum partial waves.
• Figure 4: Time series of VMI images from the non-collinear bichromatic pump-probe study of the SOWP in the $3d$ fine structure doublet mapped into the continuum by the time-delayed blue pulse in PLP configuration.