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We investigate the influence of relativistic nondipole effects on the photoelectron spectra of argon, particularly in the low kinetic energy region (0 eV - 5 eV). In our experiment, we use intense linearly polarised 800 nm laser pulse to ionise Ar from a jet and we record photoelectron energy and momentum distributions using a reaction microscope (REMI). Our measurements show that nondipole effect can cause an energy-dependent asymmetry along the laser propagation direction in the photoelectron energy and momentum spectra. Model simulation based on time-dependent Dirac equation (TDDE) can reproduce our measurement results. The electron trajectory analysis based on classical model reveals that the photoelectron which obtains negative momentum shift along laser propagation direction is caused by the interplay between the Lorenz force induced radiation pressure during its free propagation in continuum and re-scattering by Coulomb potential of the parent ion when it is driven back by the laser field., Comment: 11 pages, 15 Figures

We present a technique for generating phase-locked two-colour pulses with controllable electric field waveform, whereby the polarization states of the two frequency components, as well as their intensities, relative phase and pulse delay can be completely controlled. To characterize the phase stability and the waveform of the output two-colour pulse in situ, we measured the momentum spectra of protons from dissociative ionization of the hydrogen molecule for different combinations of polarizations.

We present a detailed experimental and theoretical study on the relativistic non-dipole effects in strong-field atomic ionisation by near-infrared linearly-polarised few-cycle laser pulses in the intensity range 1014 -1015 W/cm2. We record high-resolution photoelectron momentum distributions of argon using a reaction microscope and compare our measurements with a truly ab-initio fully relativistic 3D model based on the time-dependent Dirac equation. We observe counter-intuitive peak shifts of the transverse electron momentum distribution in the direction opposite to that of laser propagation as a function of laser intensity and demonstrate an excellent agreement between experimental results and theoretical predictions., 6 pages, 6 figures, Manuscript prepared for submission to Physical Review Letters

In strong-field ionization, the combined influence of nondipole and Coulomb focusing effects leave unique signatures on the photoelectron momentum distributions, which may have direct implications on many important strong-field phenomena. We present a comprehensive review of the experimental and theoretical investigations on these effects. We classify these investigations by relativistic and non-relativistic modelling based on different theoretical approaches, e.g. classical, semiclassical, strong-field approximation (SFA), time-dependent Schrodinger equation (TDSE), and time-dependent Dirac equation (TDDE). Finally, we discuss the latest experimental and theoretical development on this subject that has undergone so far to deeply understand the underlying physics.

Synopsis Quantum mechanical description of the relativistic non-dipole effects is of fundamental interest in strong-field physics community, as they may have direct implications on the processes relying on re-collision dynamics. Here, we present a detailed experimental and theoretical study on the relativistic non-dipole effects in strong-field ionisation at moderate intensities. We compare our precise measurements with a truly ab-initio fully relativistic 3D model based on the time-dependent Dirac equation and demonstrate an excellent agreement between experimental results and theoretical predictions.

We have investigated nuclear dynamics in bound and dissociating acetylene molecular ions in a time-resolved reaction microscopy experiment with a pair of few-cycle pulses. Vibrating bound acetylene cations or dissociating dications are produced by the first pulse. The second pulse probes the nuclear dynamics by ionization to higher charge states and Coulomb explosion of the molecule. For the bound cations, we observed vibrations in acetylene (HCCH) and its isomer vinylidene (CCHH) along the CC-bond with a periodicity of around 26 fs. For dissociating dication molecules, a clear indication of enhanced ionization is found to occur along the CH- and CC-bonds after 10 fs to 40 fs. The time-dependent ionization processes are simulated using semi-classical on-the-fly dynamics revealing the underling mechanisms.

Synopsis We present an intensity dependent study of transverse electron momentum distribution obtained from strong field ionization of argon using linearly polarized few-cycle (6 fs) laser pulses in the intensity range 1015W/cm2-1016W/cm2.