SIMULATING STRONG FIELD RESCATTERING USING ATTOSECOND LIGHT

An atom or molecule interacting with an intense, ultrafast laser pulse is a fundamental problem in modern physics. At intensities that are approximately one-tenth an atomic unit of field (50 V/A) the physics is well described by a semi-classical 3-step model where an electron tunnel ionizes, driven by the strong-field and then rescatters with its parent core. The consequence of this physics has opened the areas of attosecond science and spatial-temporal molecular imaging. However in a strong field experiment, the exponential rate of tunnel ionization fixes the release phase of the electron wave packet (EWP) at the extreme of the laser field. In this talk, we will describe a method that allows for more precise studies of the strong field process. The approach simulates the 3-step model by replacing the tunneling step with single-photon ionization by an attosecond XUV pulse. A phase-locked intense low-frequency field drives the EWP mimicking steps (2) and (3) but with little or no ionization. We will present both experimental and theoretical results demonstrating the viability of this approach

High-energy mid-infrared sub-cycle pulse synthesis from a parametric amplifier

High-energy phase-stable sub-cycle mid-infrared pulses can provide unique opportunities to explore phase-sensitive strong-field light-matter interactions in atoms, molecules and solids. At the mid-infrared wavelength, the Keldysh parameter could be much smaller than unity even at relatively modest laser intensities, enabling the study of the strong-field sub-cycle electron dynamics in solids without damage. Here we report a high-energy sub-cycle pulse synthesiser based on a mid-infrared optical parametric amplifier and its application to high-harmonic generation in solids. The signal and idler combined spectrum spans from 2.5 to 9.0 μm. We coherently synthesise the passively carrier-envelope phase-stable signal and idler pulses to generate 33 μJ, 0.88-cycle, multi-gigawatt pulses centred at ~4.2 μm, which is further energy scalable. The mid-infrared sub-cycle pulse is used for driving high-harmonic generation in thin silicon samples, producing harmonics up to ~19th order with a continuous spectral coverage due to the isolated emission by the sub-cycle driver

Laser-induced electron diffraction for probing rare gas atoms

Recently, using midinfrared laser-induced electron diffraction (LIED), snapshots of a vibrating diatomic molecule on a femtosecond time scale have been captured [C. I. Blaga et al., Nature (London) 483, 194 (2012)]. In this Letter, a comprehensive treatment for the atomic LIED response is reported, a critical step in generalizing this imaging method. Electron-ion differential cross sections (DCSs) of rare gas atoms are extracted from measured angular-resolved, high-energy electron momentum distributions generated by intense midinfrared lasers. Following strong-field ionization, the high-energy electrons result from elastic rescattering of a field-driven wave packet with the parent ion. For recollision energies 100 eV, the measured DCSs are indistinguishable for the neutral atoms and ions, illustrating the close collision nature of this interaction. The extracted DCSs are found to be independent of laser parameters, in agreement with theory. This study establishes the key ingredients for applying LIED to femtosecond molecular imaging

High-harmonic generation in solids using a mid-infrared sub-cycle pulse synthesizer

We generate high-order harmonics in silicon using a mid-infrared (2.5−9.0 μm) pulse synthesizer. Even and odd harmonics (~19$^{th}$ order) with few-cycle pulses and near-continuous spectra with sub-cycle pulses, indicating an isolated harmonic emission, are observed

High-harmonic emission in solids driven by mid-infrared sub-cycle pulses

High-harmonic generation in silicon driven by mid-infrared pulses at 2.5−9.0 μm is reported. We observe even and odd harmonics (~19th order) with few-cycle pulses and near-continuous spectra with sub-cycle pulses, indicating an isolated harmonic emission