Dissociative photoionization of NO across a shape resonance in the XUV range using circularly polarized synchrotron radiation.

We report benchmark results for dissociative photoionization (DPI) spectroscopy and dynamics of the NO molecule in the region of the σ* shape resonance in the ionization leading to the NO+(c3Π) ionic state. The experimental study combines well characterized extreme ultraviolet (XUV) circularly polarized synchrotron radiation, delivered at the DESIRS beamline (SOLEIL), with ion-electron coincidence 3D momentum spectroscopy. The measured (N+, e) kinetic energy correlation diagrams reported at four discrete photon energies in the extended 23-33 eV energy range allow for resolving the different active DPI reactions and underline the importance of spectrally resolved studies using synchrotron radiation in the context of time-resolved studies where photoionization is induced by broadband XUV attosecond pulses. In the dominant DPI reaction which leads to the NO+(c3Π) ionic state, photoionization dynamics across the σ* shape resonance are probed by molecular frame photoelectron angular distributions where the parallel and perpendicular transitions are highlighted, as well as the circular dichroism CDAD(θe) in the molecular frame. The latter also constitute benchmark references for molecular polarimetry. The measured dynamical parameters are well described by multichannel Schwinger configuration interaction calculations. Similar results are obtained for the DPI spectroscopy of highly excited NO+ electronic states populated in the explored XUV photon energy range

Circular dichroism in molecular-frame photoelectron angular distributions in the dissociative photoionization of H2 and D2 molecules

ABSTRACT: The presence of net circular dichroism in the photoionization of nonchiral homonuclear molecules has been put in evidence recently through the measurement of molecular-frame photoelectron angular distributions in dissociative photoionization of H2 [Dowek et al., Phys. Rev. Lett. 104, 233003 (2010)]. In this work we present a detailed study of circular dichroism in the photoelectron angular distributions of H2 and D2 molecules, oriented perpendicularly to the propagation vector of the circularly polarized light, at different photon energies (20, 27, and 32.5 eV). Circular dichroism in the angular distributions at 20 and to a large extent 27 eV exhibits the usual pattern in which inversion symmetry is preserved. In contrast, at 32.5 eV, the inversion symmetry breaks down, which eventually leads to total circular dichroism after integration over the polar emission angle. Time-dependent ab initio calculations support and explain the observed results for H2 in terms of quantum interferences between direct photoionization and delayed autoionization from the Q1 and Q2 doubly excited states into ionic states (1sσg and 2pσu) of different inversion symmetry. Nevertheless, for D2 at 32.5 eV, there is a particular case where theory and experiment disagree in the magnitude of the symmetry breaking: when D+ ions are produced with an energy of around 5 eV. This reflects the subleties associated to such simple molecules when exposed to this fine scrutiny

Optics-free ffocusing and application to spectral filtering of XUV beam

Poster session III (Tu4A)International audienceWe experimentally characterize XUV intensity profiles and wavefronts, and demonstrate XUV beams focusing without resorting any optics. We use this coherent effect to spectrally filter group of harmonics. Simulations show possible control of attosecond temporal structure

Optics-free focusing down to micrometer spot size and spectral filtering of XUV harmonics

Controlling the wavefront of an extreme ultraviolet (XUV) high-order harmonic beam during the generation process offers to focus the beam without resorting to any XUV optics. By characterizing the XUV intensity profile and wavefront, we quantitatively retrieve both the size and the position of the waist of each generated harmonics and show that optics-free focusing leads to focused XUV spot with micrometer size. We use this remarkable coherent effect to demonstrate efficient and adjustable spectral filtering of the XUV light, along with a strong rejection of the fundamental beam, without using any XUV optics

Spectral filtering of high-order harmonics via optics-free focusing

Controlling the wavefront of an extreme ultraviolet (XUV) high-order harmonic beam during the generation process offers the capability of modifying the beam properties without resorting to any XUV optics. By characterizing the XUV intensity profile and wavefront, we quantitatively retrieve both the size and the position of the waist of each harmonic generated in an argon jet. We show that optics-free focusing can occur under specific generating conditions leading to XUV focii of micrometer size. We also demonstrate that each focus is located at distinct longitudinal positions. Using this remarkable XUV wavefront control combined with near focus spatial selection, we experimentally demonstrate efficient and adjustable spectral filtering of the XUV beam, along with a strong rejection of the fundamental beam, without using any XUV optics. The experimental results are compared with simulations providing the impact of the filtering on the temporal profile of the XUV field. It shows that the attosecond structure is preserved and that the beam is more homogeneous after the filtering, thereby reducing the longitudinal focii shift. This is a major step to achieve high XUV intensity and probing ultrafast processes with an improved resolution

Spatiotemporal control of attosecond XUV beams

International audienceSpectral and spatial control of XUV beams is demonstrated combining divergence control at the generating plane with intermediate-field spatial filtering. This control is reproduced by simulations and shows a net improvement of attosecond beam homogeneity

A quantum molecular movie polyad predissociation dynamics in the VUV excited 3p sigma Rydberg state of nitrogen dioxide

The optical formation of coherent superposition states, a wavepacket, can allow the study of zeroth order states, the evolution of which exhibit structural and electronic changes as a function of time this leads to the notion of a molecular movie. Intramolecular vibrational energy redistribution, due to anharmonic coupling between modes, is the molecular movie considered here. There is no guarantee, however, that the formed superposition will behave semi classically e.g. Gaussian wavepacket dynamics or even as an intuitively useful zeroth order state. Here we present time resolved photoelectron spectroscopy TRPES studies of an electronically excited triatomic molecule wherein the vibrational dynamics must be treated quantum mechanically and the simple picture of population flow between coupled normal modes fails. Specifically, we report on vibronic wavepacket dynamics in the zeroth order 3p amp; 963;2 amp; 931;u Rydberg state of NO2. This wavepacket exemplifies two general features of excited state dynamics in polyatomic molecules anharmonic multimodal vibrational coupling forming polyads ; nonadiabatic coupling between nuclear and electronic coordinates, leading to predissociation. The latter suggests that the polyad vibrational states in the zeroth order 3p Rydberg manifold are quasi bound and best understood to be scattering resonances. We observed a rapid dephasing of an initially prepared bright valence state into the relatively long lived 3p Rydberg state whose multimodal vibrational dynamics and decay we monitor as a function of time. Our quantum simulations, based on an effective spectroscopic Hamiltonian, describe the essential features of the multimodal Fermi resonance driven vibrational dynamics in the 3p state. We also present evidence of polyad specificity in the state dependent predissociation rates, leading to free atomic and molecular fragments. We emphasize that a quantum molecular movie is required to visualize wavepacket dynamics in the 3p amp; 963;2 amp; 931;u Rydberg state of NO