Strong-Field Physics with Mid-IR Fields

Abstract

Strong-field physics is currently experiencing a shift towards the use of mid-IR driving wavelengths. This is because they permit conducting experiments unambiguously in the quasistatic regime and enable exploiting the effects related to ponderomotive scaling of electron recollisions. Initial measurements taken in the mid-IR immediately led to a deeper understanding of photoionization and allowed a discrimination among different theoretical models. Ponderomotive scaling of rescattering has enabled new avenues towards time-resolved probing of molecular structure. Essential for this paradigm shift was the convergence of two experimental tools: (1) intense mid-IR sources that can create high-energy photons and electrons while operating within the quasistatic regime and (2) detection systems that can detect the generated highenergy particles and image the entire momentum space of the interaction in full coincidence. Here, we present a unique combination of these two essential ingredients, namely, a 160-kHz mid-IR source and a reaction microscope detection system, to present an experimental methodology that provides an unprecedented three-dimensional view of strong-field interactions. The system is capable of generating and detecting electron energies that span a 6 order of magnitude dynamic range. We demonstrate the versatility of the system by investigating electron recollisions, the core process that drives strong-field phenomena, at both low (meV) and high (hundreds of eV) energies. The low-energy region is used to investigate recently discovered low-energy structures, while the high-energy electrons are used to probe atomic structure via laser-induced electron diffraction. Moreover, we present, for the first time, the correlated momentum distribution of electrons from nonsequential double ionization driven by mid-IR pulses.

The plateau in above-threshold ionization: the keystone of rescattering physics

“…Following its discovery various additional spectral features at comparatively low energies have been identified: a very lowenergy structure (VLES) significantly below the LES [71], a zero-energy structure (ZES) [72,73], a 'V' structure [74][75][76], as well as other patterns in the velocity map at low-energy. All but the VLES can be attributed to low-energy rescattering, but other mechanisms have been discussed as well.…”

Recollision as a probe of magnetic-field effects in nonsequential double ionization

“…Mid-infrared laser-fields are chosen because magnetic field effects set in for small intensities, see Fig. 1, attracting a lot of interest in recent years [15,16].…”

R-matrix-incorporating-time method forH2+in short and intense laser fields

“…The construction of Free-Electron laser (FEL) sources capable of delivering unprecedented intense radiation in the soft and hard X-ray regimes has initiated new challenges, not only within atomic, molecular and optical physics but also for a number of other areas at the forefront of current interest more broadly, such as in biology, chemistry and nanoscience. Recently, another advancement on the opposite end of the wavelength regime, has been the increased availability of intense mid-IR range radiation [1]. In parallel with the aforementioned recent advances in strong-field physics the production of ultra-short pulses of sub-femtosecond duration has allowed the direct experimental observation of electronic and structural dynamics in matter [2].…”