Dong-Sheng Guo

The calculation of photoelectron angular distributions with jet-like structure from scattering theory

Photoelectron angular distributions produced in above-threshold ionization (ATI) are analysed using a nonperturbative scattering theory. The numerical results are in good qualitative agreement with recent measurements. Our study shows that the origin of the jet-like structure arises from the inherent properties of the ATI process and not from the angular momentum of either the initial or the excited states of the atom.

A scaling law of photoionization in few-cycle regime.

In this paper, a scaling law of photoionization of atoms irradiated by intense, few-cycle laser pulses is established. The scaling law sets a relation to the phase-dependent ionization with the kinetic energy of photoelectrons, the duration and peak intensity of short pulses, and the ionization potential of the target atoms. We find that it will be advantageous to manifest the phase-dependent photoionization by choosing the target atoms with larger ionization potential, using laser with smaller carrier-frequency, and increasing the pulse intensity.

Angular splitting in half Kapitza-Dirac effect of H+2 molecules

The half Kapitza-Dirac effect following photoionization of molecules in intense standing-wave laser fields is studied. Photoelectron angular distributions (PADs) of molecules split towards the laser propagation and exhibit multiple splitting, which manifests the integer property of the ponderomotive parameter, as the laser intensity increases. The PADs are asymmetric about the laser polarization plane and vary with the molecular alignment as well as the kinetic energy of photoelectrons.

Jet-like structure in photoelectron angular distributions

Photoelectron angular distributions produced in above-threshold ionization are analyzed using a nonperturbative scattering theory. The numerical results show good agreement with recent measurements and predicted new features to be observed. Our study shows that the origin of the jet-like structure arises from the inherent properties of the ATI process.

Beam profiler for single-photon applications based on compressive sampling techniques

We report the development of a low-cost beam characterization technique appropriate for extremely low light levels. The technique makes use of compressive sampling strategies that have been developed recently for imaging applications.

Half Kapitza-Dirac effect of H2+ molecule in intense standing-wave laser fields

The half Kapitza-Dirac effect of H2+ molecule in an intense standing-wave laser field is studied with a focus on the influence of the molecular orbital symmetry and the molecular alignment on the photo-electron angular distributions (PADs). In standing-wave laser fields, the PADs split along the scattering angle due to the momentum change of electron with photons when it escapes from the laser fields. The structures and the symmetry of PADs are severely affected by the molecular orbital symmetry and the molecular alignment. For H2+ molecule in ground state (σg), the PADs are severely changed by the molecular alignment only when the photoelectron kinetic energy is sufficiently high. For H2+ molecule in the first excited state (σμ), the molecular alignment distinctively changes the PADs, irrelevant to the kinetic energy of photoelectrons. When the molecules are aligned either parallel with or perpendicular to the laser polarization, the PADs are symmetric about an axis. In other cases, the PADs do not show any symmetry. These results indicate that the molecular alignment can be used to control the splitting in the half Kapitza-Dirac effect.

Scaling law for energy-momentum spectra of atomic photoelectrons

A scaling law which was used to classify photoelectron angular distributions (PADs) is now extended to photoelectron kinetic energy spectra. Both a theoretical proof and an independent verification are presented. Considering PADs are of photoelectron momentum spectra, this extension really extends the scaling law to the entire energy-momentum spectra. The scaling law for photoelectron energy-momentum spectra applies to both directly ionized and rescattered photoelectrons. Re-scaling experimental input parameters without loosing the physical essence with this scaling law may ease the experimental conditions and reduce the material and the energy consumptions in the experiments.

Theory for Generation of High Harmonics in the Electron Exit Process

Experiments manifested that plasma interacting with a strong laser field can produce both even and odd high harmonics. Applying a nonperturbative quantum electrodynamics theory, we treat plasma states in a laser field as Volkov states. Our study shows when charged particles exit the single‐mode laser field, spontaneous emissions as high harmonics with both even and odd orders occur due to the energy‐momentum conservation. In multiphoton ionization (MPI) Volkov states play a role as intermediate states subject to a subsequent transition to plane waves according to the scattering theory of Guo, Aberg, and Crasemann (GAC). We identify the intermediate Volkov states in MPI as plasma states. By applying Gao et al.’s recent formula for MPI, derived from GAC theory with the inclusion of spontaneous emissions, we obtain spectra for high harmonics with both even and odd orders generated in the photoelectron exit process.

Formal scattering approach to high-order harmonic generation

By using the time-independent formal scattering theoretical approach, we develop a nonperturbative quantum electrodynamics theory to describe high-order harmonic generation (HHG). This theory recovers the semi-classical interpretation of Corkum (Phys. Rev. Lett. 71 (1993) 1994) and gives the same phenomenological cutoff law. The HHG emission rate is expressed as an analytic closed form. We also discuss the connection between HHG and the above threshold ionization from the scattering viewpoint.