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Abstract: We introduce a novel in-situ method that utilizes momentum microscopy via single-atom ionization to capture the electric field of a femtosecond laser pulse.
Studying ultrafast, strong-field-driven phenomena in atoms and molecules is central to attosecond science, enabling direct access to electron dynamics on sub-cycle time scales. Reaction Microscopy, also known as Cold Target Recoil-Ion Momentum Spectroscopy (COLTRIMS), provides coincidence three-dimensional momentum measurements of photoelectrons and ions and has become a cornerstone technique for probing ultrafast processes. Since many field-driven processes evolve on a sub-cycle time scale, the complete characterization of the ionizing pulse is a critical aspect of many ultrafast photoionization experiments. Near infrared femtosecond laser technology has been the main driver of ultrafast photoionization science for the past two decades. However, most currently available near-infrared pulse characterization techniques that rely on nonlinear optical effects (e.g., FROG, SPIDER, D-scan) are primarily sensitive to the intensity envelope and do not provide information about the sub-cycle temporal evolution of the pulse. Strong-field ionization-based approaches offer direct sensitivity to the electric field waveform but are typically implemented ex situ and may require dedicated vacuum systems or auxiliary sampling pulses.
Tunneling Ionization with a Perturbation for the Time-domain Observation of an Electric Field (TIPTOE) enables sub-cycle sampling of arbitrary light waveforms in gases and solids. Here, we extend TIPTOE to the single-atom ionization regime inside a COLTRIMS spectrometer, enabling true in-situ waveform characterization. In our setup an intense, near-infrared femtosecond laser pulse is split into an intense, ionizing pulse and a weak, but otherwise identical, sampling pulse. The delay-dependent modulation of the ionization yield directly maps to the electric field of the sampling pulse. In addition, the photoelectron momentum distribution also provides direct access to the vector potential of the laser pulse. In summary we present a novel in-situ technique that combines COLTRIMS and TIPTOE to sample electric field waveforms via momentum microscopy using single-atom ionization. This approach offers a new level of control for studies of strong-field dynamics using photoionization coincidence momentum spectroscopy.
| Keyword-1 | Strong-field physics |
|---|---|
| Keyword-2 | COLTRIMS |