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Understanding the fundamentals of laser-matter interactions is crucial for developing and optimizing ultrafast laser processing strategies. In optically transparent solids, the key event by which energy is deposited in the material is through the generation of an electron–hole plasma via nonlinear excitation mechanisms. As the energy stored in the plasma relaxes, local distortions of the lattice may occur, such as point defects. These defects give rise to new discrete energy states located in the bandgap. In this study, we investigate how the presence of these energy states influences the transmission of ultrashort near-infrared laser pulses in fused silica. Experimental results of laser pulse transmission and photoluminescence from defects are correlated with optical microscopy of the irradiated spots, allowing us to identify different nonlinear interaction regimes. Numerical simulations indicate that photo-induced defects influence the nonlinear losses of ultrashort laser pulses and explain why a non-destructive damage regime with detectable excitation is only observed for a narrow intensity range in multipulse experiments. [ABSTRACT FROM AUTHOR]

Measurements on the strong-field ionization of carbonyl sulfide molecules by short, intense, 2 µm wavelength laser pulses are presented from experiments where angle-resolved photoelectron distributions were recorded with a high-energy velocity map imaging spectrometer, designed to reach a maximum kinetic energy of 500 eV. The laser-field-free elastic-scattering cross section of carbonyl sulfide was extracted from the measurements and is found in good agreement with previous experiments, performed using conventional electron diffraction. By comparing our measurements to the results of calculations, based on the quantitative rescattering theory, the bond lengths and molecular geometry were extracted from the experimental differential cross sections to a precision better than ±5 pm and in agreement with the known values. [ABSTRACT FROM AUTHOR]

The time-resolved photodynamics of the methyl iodide cation (CH3I+) are investigated by means of femtosecond XUV–IR pump–probe spectroscopy. A time-delay-compensated XUV monochromator is employed to isolate a specific harmonic, the 9th harmonic of the fundamental 800 nm (13.95 eV, 88.89 nm), which is used as a pump pulse to prepare the cation in several electronic states. A time-delayed IR probe pulse is used to probe the dissociative dynamics on the first excited state potential energy surface. Photoelectrons and photofragment ions— and I+—are detected by velocity map imaging. The experimental results are complemented with high level ab initio calculations for the potential energy curves of the electronic states of CH3I+ as well as with full dimension on-the-fly trajectory calculations on the first electronically excited state , considering the presence of the IR pulse. The and I+ pump–probe transients reflect the role of the IR pulse in controlling the photodynamics of CH3I+ in the state, mainly through the coupling to the ground state and to the excited state manifold. Oscillatory features are observed and attributed to a vibrational wave packet prepared in the state. The IR probe pulse induces a coupling between electronic states leading to a slow depletion of fragments after the cation is transferred to the ground states and an enhancement of I+ fragments by absorption of IR photons yielding dissociative photoionization. [ABSTRACT FROM AUTHOR]

We present a novel soft x-ray spectrometer for ultrafast absorption spectroscopy utilizing table-top femtosecond high-order harmonic sources. Where most commercially available spectrometers rely on spherical variable line space gratings with a typical efficiency on the order of 3% in the first diffractive order, this spectrometer, based on a Hettrick–Underwood design, includes a reflective zone plate as a dispersive element. An improved efficiency of 12% at the N K-edge is achieved, accompanied by a resolving power of 890. The high performance of the soft x-ray spectrometer is further demonstrated by comparing nitrogen K-edge absorption spectra from calcium nitrate in aqueous solution obtained with our high-order harmonic source to previous measurements performed at the electron storage ring facility BESSY II. [ABSTRACT FROM AUTHOR]

We present a time-resolved study of the photodissociation dynamics of OCS after UV-photoexcitation at λ = 237 nm. OCS molecules (X1Σ+) were primarily excited to the 11A′′ and the 21A′ Renner–Teller components of the 1Σ− and 1Δ states. Dissociation into CO and S fragments was observed through time-delayed strong-field ionisation and imaging of the kinetic energy of the resulting CO+ and S+ fragments by intense 790 nm laser pulses. Surprisingly, fast oscillations with a period of ∼100 fs were observed in the S+ channel of the UV dissociation. Based on wavepacket-dynamics simulations coupled with a simple electrostatic-interaction model, these oscillations do not correspond to the known highly-excited rotational motion of the leaving CO(X1Σ+, J ≫; 0) fragments, which has a timescale of ∼140 fs. Instead, we suggest to assign the observed oscillations to the excitation of vibrational wavepackets in the 23A′′ or 21A′′ states of the molecule that predissociate to form S(3PJ) photoproducts. [ABSTRACT FROM AUTHOR]

Valence band photoionization of CO2 has been studied by photoelectron spectroscopy using a velocity map imaging spectrometer and synchrotron radiation. The measured data allow retrieving electronic and vibrational branching ratios, vibrationally resolved asymmetry parameters, and the total electron yield which includes multiple strong resonances. Additionally, the spectrum of low kinetic energy electrons has been studied in the resonant region, and the evolution with photon energy of one of the forbidden transitions present in the slow photoelectrons spectrum has been carefully analyzed, indicating that in the presence of auto-ionizing resonances the vibrational populations of the ion are significantly redistributed. [ABSTRACT FROM AUTHOR]

The development of attosecond pump–probe experiments at high repetition rate requires the development of novel attosecond sources maintaining a sufficient number of photons per pulse. We use 7 fs, 800 nm pulses from a non-collinear optical parametric chirped pulse amplification laser system to generate few-pulse attosecond pulse trains (APTs) with a flux of >106 photons per shot in the extreme ultraviolet at a repetition rate of 100 kHz. The pulse trains have been fully characterised by recording frequency-resolved optical gating for complete reconstruction of attosecond bursts (FROG-CRAB) traces with a velocity map imaging spectrometer. For the pulse retrieval from the FROG-CRAB trace a new ensemble retrieval algorithm has been employed that enables the reconstruction of the shape of the APTs in the presence of carrier envelope phase fluctuations of the few-cycle laser system. [ABSTRACT FROM AUTHOR]

The electric field of attosecond laser pulses can be retrieved from laser-dressed photoionisation measurements, where electron wavepackets that result from single-photon ionisation by the attosecond pulse in the presence of a dressing field are produced. In case of fluctuating dressing laser and/or attosecond pulses, e.g. due to pulse-to-pulse fluctuations of the carrier envelope phase of the infrared laser pulse, commonly applied retrieval algorithms result in the erroneous extraction of the pulse fields. We present a mixed state time-domain ptychography algorithm for the retrieval of pulse ensembles from attosecond streaking experiments. [ABSTRACT FROM AUTHOR]

The development of schemes for coherent nonlinear time-domain spectroscopy in the extreme-ultraviolet regime (XUV) has so far been impeded by experimental difficulties that arise at these short wavelengths. In this work we present a novel experimental approach, which facilitates the timing control and phase cycling of XUV pulse sequences produced by harmonic generation in rare gases. The method is demonstrated for the generation and high spectral resolution characterization of narrow-bandwidth harmonics (≈14 eV) in argon and krypton. Our technique simultaneously provides high phase stability and a pathway-selective detection scheme for nonlinear signals—both necessary prerequisites for all types of coherent nonlinear spectroscopy. [ABSTRACT FROM AUTHOR]

An extreme-ultraviolet (XUV) laser pulse consisting of harmonics of a fundamental near-infrared (NIR) laser frequency is combined with the NIR pulse to systematically study two-color photoionization of helium atoms. A time-resolved photoelectron spectroscopy experiment is carried out where energy- and angle-resolved photoelectron distributions are obtained as a function of the NIR intensity and wavelength. Time-dependent Schrödinger equation calculations are performed for the conditions corresponding to the experiment and used to extract residual populations of Rydberg states resulting from excitation by the XUV + NIR pulse pair. The residual populations are studied as a function of the NIR intensity (3.5 × 1010 − 8 × 1012 W cm−2) and wavelength (760–820 nm). The evolution of the photoelectron distribution and the residual populations are interpreted using an effective restricted basis model, which includes the minimum set of states relevant to the features observed in the experiments. As a result, a comprehensive and intuitive picture of the laser-induced dynamics in helium atoms exposed to a two-color XUV–NIR light field is obtained. [ABSTRACT FROM AUTHOR]

We report on a combined experimental and theoretical study of XUV ionization of atomic argon in the presence of a near-infrared (NIR) laser field. Using a table-top source of wavelength-selected femtosecond XUV pulses in combination with a velocity map imaging spectrometer we record angle- and energy-resolved photoelectron distributions and simulate the experimental data by solving the time-dependent Schrödinger equation ab initio. In order to compare with the experimental data we average the calculated energy-angle probability distributions over the experimental focal volume for different values of the magnetic quantum number of the photoelectron. This averaging procedure washes out the intracycle interference pattern, which would otherwise be observed in the form of angular modulations of the photoelectron spectra. We recover these modulations experimentally and in the simulations by evaluating the difference between two averaged distributions that are obtained for slightly different NIR laser field intensities. [ABSTRACT FROM AUTHOR]

A recent experiment (Villeneuve et al 2017 Science 356 1150) has shown that two-color photoionization of neon by the combination of an attosecond XUV pulse train and a moderately strong, linearly polarized IR pulse can preferentially produce photoelectrons with orbital angular quantum number l = 3 (f-wave) and magnetic quantum number m = 0. This result was rationalized by the occurrence of different Stark shifts of m = 0 and |m| = 1 sub-levels in the IR laser field. Here we perform 3D time-dependent Schrödinger equation calculations with a neon effective potential to identify the mechanism for the selective excitation and ionization of m = 0 sub-levels. Calculations of the ionization and excitation yields as a function of the IR intensity and the XUV and IR photon energy reveal that a coupling between two dominant ionization channels involving 3p and 3d intermediate excitations is responsible for the observed m-level selectivity. We compare calculated and measured photoelectron velocity map images and ionization yields over a range of IR intensities and XUV and IR photon energies, and confirm that the m = 0 or |m| = 1 channel, and thus a single set of the quantum numbers, (Jion, l, m), can be selected by an appropriate choice of these parameters. [ABSTRACT FROM AUTHOR]

Reports on results of an experimental and theoretical study of nonadiabatic wave packet dynamics in the intermediate coupling regime. Use of a femtosecond pump-probe molecular beam technique to generate a wave packet which evolves on the electronically excited coupled states; Systematic variation of the pump laser wavelength.

Results are presented of calculations on the experimentally observed lifetime enhancement of high principal quantum number nf(N+=2) and np(N+=0) Rydberg states of the NO molecule in small dc electric fields. A Hund’s case (d) molecular Hamiltonian is introduced, which describes intramolecular interactions between low angular momentum Rydberg states as a result of core penetration and l mixing caused by the electric field. Eigenstates of the molecule in the electric field are obtained by diagonalization of the Hamiltonian and an effective decay time is determined which describes the multiexponential decay of the superposition of (Stark) states which is excited experimentally. The calculations reproduce the striking onset of the lifetime enhancement of the np(N+=0) series, which was observed experimentally. Both for the nf(N+=2) and np(N+=0) Rydberg series, core penetration by low-l states leads to extensive interseries coupling for several values of the principal quantum number. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present results of fs pump–probe experiments on the predissociation dynamics of the IBr B-state, as a model of nonadiabatic wave packet dynamics on coupled potential energy curves. The observations reflect the complicated wave packet motion on the coupled potentials and oscillatory behavior of the decay rates as a function of excitation energy. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Evidence for lifetime enhancement of Rydberg states by interactions with surrounding ions is obtained from femtosecond pump–probe experiments on the vibrational wave packet dynamics of the I2(B)-state, in which either detection of I+2 ions or zero-kinetic energy (ZEKE) electrons was used. The use of the ZEKE technique leads to the appearance of new frequency components in the Fourier transform power spectra of pump–probe time delay scans, as well as the observation of enhanced peak-to-valley ratios in these scans. These observed frequency components do not correspond to any energy level spacings in the molecule; they correspond to a sum of two energy level spacings, suggesting a nonlinear detection mechanism in the ZEKE technique (i.e., interaction with ions). Additional evidence for our interpretation is presented through experiments in which additional ions were formed through nonresonant multiphoton ionization of I2 with a picosecond 266 nm laser, as well as experiments in which both the decay time of the ZEKE signal and the appearance of the pump–probe time delay scans as a function of the pulsed field time delay were studied. Theoretical wave packet calculations which support the conclusions are presented. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Lifetime measurements are reported for high principal quantum number (n=43–87) autoionizing Rydberg states of the Xe atom, prepared using state-selective excitation with a narrow bandwidth laser. It is demonstrated that the lifetimes can be increased by l-mixing in dc electric fields, as well as by l,m-mixing through the presence of surrounding Xe+ ions. The influence of l,m-mixing interactions on the peak intensities in zero-electron-kinetic-energy (ZEKE) photoelectron spectroscopy experiments is discussed, and a possible method for increasing the applicability of ZEKE experiments is suggested. In addition, experimental evidence is given for spin–orbit state changing Xe*(n)–Xe collisions. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Lifetime measurements are reported for high principal quantum number (n=40–125) Rydberg states of the NO molecule, prepared using state-selective double resonance excitation with a narrow bandwidth laser. The influence of (i) the application of a dc electric field, and (ii) interactions of the Rydberg states with surrounding ions, were investigated. It is demonstrated that the presence of dc electric fields can lead to enhancements in the lifetimes due to l-mixing, and the conclusion is reached that under the conditions existing in a typical zero-electron-kinetic-energy (ZEKE) photoelectron spectroscopy experiment, the Rydberg states involved are excited in a regime where l-mixing is expected to be significant. It is observed that l- and m-mixing collisional interactions provide a further mechanism to stabilize the optically prepared Rydberg states, beyond the limits which can be achieved by l-mixing alone. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Femtosecond pump–probe zero-kinetic-energy (ZEKE) photoelectron spectroscopy is studied using the known wave-packet dynamics of I2 (B state). The 340 fs wave-packet period, wave-packet dephasing and rephasing are observed in the ZEKE signal. The effect of various laser and ZEKE parameters on the wave-packet dynamics is discussed. [ABSTRACT FROM AUTHOR]

We study the Strong-Field Ionization (SFI) of the hydrocarbon 1-butene as a function of wavelength using photoion-photoelectron covariance and coincidence spectroscopy. We observe a striking transition in the fragment-associated photoelectron spectra: from a single Above Threshold Ionization (ATI) progression for photon energies less than the cation D0–D1 gap to two ATI progressions for a photon energy greater than this gap. For the first case, electronically excited cations are created by SFI populating the ground cationic state D0, followed by sequential post-ionization excitation. For the second case, direct sub-cycle SFI to the D1 excited cation state contributes significantly. Our experiments access ionization dynamics in a regime where strong-field and resonance-enhanced processes can interplay. [ABSTRACT FROM AUTHOR]

An autoionizing resonance in molecular N2 is excited by an ultrashort XUV pulse and probed by a subsequent weak IR pulse, which ionizes the contributing Rydberg states. Time- and angular-resolved photoelectron spectra recorded with a velocity map imaging spectrometer reveal two electronic contributions with different angular distributions. One of them has an exponential decay rate of 20 ± 5 fs, while the other one is shorter than 10 fs. This observation is interpreted as a manifestation of interference stabilization involving the two overlapping discrete Rydberg states. A formalism of interference stabilization for molecular ionization is developed and applied to describe the autoionizing resonance. The results of calculations suggest, that the effect of the interference stabilization is facilitated by rotationally-induced couplings of electronic states with different symmetry. [ABSTRACT FROM AUTHOR]

The emerging application of attosecond techniques to molecular systems allows the role of electronic coherence in the control of chemical reactions to be investigated. Prompt ionization of molecules by an attosecond pulse may induce charge migration across a molecular structure on attosecond to few-femtosecond timescales, thereby possibly determining the subsequent relaxation pathways that a molecule may take. We discuss how proposals for this 'charge-directed reactivity' fit within the current understanding of quantum control and review the current state of the art of attosecond molecular science. Specifically, we review the role of electronic coherence and coupling of the electronic and nuclear degrees of freedom in high-harmonic spectroscopy and in the first attosecond pump-probe experiments on molecular systems. [ABSTRACT FROM AUTHOR]

The article presents the authors' comments on various issues related to attosecond science. It is stated that scientists are now able to manipulate electrons by using laser fields, that allows them to research recollision physics and ionization dynamics on attosecond timescales. It is mentioned that quantum electrodynamics, which describes light in terms of photons, is necessary for analysing time-resolved X-ray scattering patterns.

The natural timescale for electron dynamics reaches down to the attosecond domain. Following the discovery of attosecond laser pulses, about a decade ago, attosecond science has developed into a vibrant, new research field, where the motion of single or multiple electrons and, in molecules, the coupling of electronic and nuclear motion, can be investigated, on attosecond to few-femtosecond timescales. Attosecond experiments require suitable observables. This review describes how “attosecond imaging”, basing itself on kinetic energy and angle-resolved detection of photoelectrons and fragment ions using a velocity map imaging (VMI) spectrometer, has been exploited in a number of pump–probe experiments. The use of a VMI spectrometer in attosecond experiments has allowed the characterization of attosecond pulse trains and isolated attosecond pulses, the elucidation of continuum electron dynamics and wave packet interferometry in atomic photoionization and the observation of electron localization in dissociative molecular photoionization. [ABSTRACT FROM AUTHOR]

We present an experimental and theoretical investigation of the angular distributions of electrons ejected in aligned molecules by extreme ultra-violet ionization using a high harmonic generation (HHG) source. Impulsive alignment in O2, N2 and CO molecules was achieved using a near-IR laser pulse and the photoelectron angular distribution after ionization by a fs harmonic comb composed of harmonic H11 to H29 (17.5-46 eV) was recorded at the maximum of both alignment and anti-alignment. The experiment reveals signatures that are specific for the electronic orbitals that are ionized as well as the onset of the influence of the molecular structure and is well reproduced by theoretical calculations based on the multichannel Schwinger configuration interaction method. [ABSTRACT FROM AUTHOR]

Recent advances in the generation and characterization of extreme-ultraviolet pulses, generated either by intense femtosecond lasers or by free electron lasers, are pushing the frontier of time-resolved investigations down to the attosecond domain, the relevant timescale for electron motion. The quantum nature of the intertwined electronic and nuclear motion requires theoretical models going beyond the Born–Oppenheimer approximation and taking into account electron correlation, representing a challenge for the computational power available nowadays. Understanding how the electron dynamics inside molecules can influence chemical reactions presents important implications in several fields and allows for the development of new technologies. In this paper, we report on experimental and theoretical results of an investigation in H_2/D_2, where for the first time control of molecular dynamics with attosecond resolution was achieved. The data represent the first evidence of the control of the electron motion in a molecule undergoing a chemical reaction on the subfemtosecond scale. [ABSTRACT FROM PUBLISHER]

Collective electron motion in condensed matter typically unfolds on a sub-femtosecond timescale. The well-defined electric field evolution of intense, phase-stable few-cycle laser pulses provides an ideal tool for controlling this motion. The resulting manipulation of local electric fields at nanometre spatial and attosecond temporal scales offers unique spatio-temporal control of ultrafast nonlinear processes at the nanoscale, with important implications for the advancement of nanoelectronics. Here we demonstrate the attosecond control of the collective electron motion and directional emission from isolated dielectric (SiO2) nanoparticles with phase-stabilized few-cycle laser fields. A novel acceleration mechanism leading to the ejection of highly energetic electrons is identified by the comparison of the results to quasi-classical model calculations. The observed lightwave control in nanosized dielectrics has important implications for other material groups, including semiconductors and metals. [ABSTRACT FROM AUTHOR]

The use of a new type in-vacuum pixel detector in velocity map imaging (VMI) is introduced. The Medipix2 and Timepix semiconductor pixel detectors (256×256 square pixels, 55×55 μm2) are well suited for charged particle detection. They offer high resolution, low noise, and high quantum efficiency. The Medipix2 chip allows double energy discrimination by offering a low and a high energy threshold. The Timepix detector allows to record the incidence time of a particle with a temporal resolution of 10 ns and a dynamic range of 160 μs. Results of the first time application of the Medipix2 detector to VMI are presented, investigating the quantum efficiency as well as the possibility to operate at increased background pressure in the vacuum chamber. [ABSTRACT FROM AUTHOR]

Manipulation of the molecular-axis distribution is an important ingredient in experiments aimed at understanding and controlling molecular processes. Samples of aligned or oriented molecules can be obtained following the interaction with an intense laser field, enabling experiments in the molecular rather than the laboratory frame. However, the degree of impulsive molecular orientation and alignment that can be achieved using a single laser field is limited and crucially depends on the initial states, which are thermally populated. Here we report the successful demonstration of a new technique for laser-field-free orientation and alignment of molecules that combines an electrostatic field, non-resonant femtosecond laser excitation and the preparation of state-selected molecules using a hexapole. As a unique quantum-mechanical wavepacket is formed, a large degree of orientation and alignment is observed both during and after the femtosecond laser pulse, which is even further increased (to 〈cosθ〉=−0.74 and 〈cos2θ〉=0.82, respectively) by tailoring the shape of the femtosecond laser pulse. This work should enable new applications such as the study of reaction dynamics or collision experiments in the molecular frame, and orbital tomography of heteronuclear molecules. [ABSTRACT FROM AUTHOR]

We describe the recent emergence of attosecond science, assessing the present state of the art and discussing several recent examples where attosecond electron dynamics has been studied in atomic and molecular systems. After introducing the generation and characterization of attosecond laser pulses, we describe the use of isolated attosecond pulses in a pump-probe experiment revealing the subcycle time dependence of a multiphoton ionization process and an experiment using the interference from a train ofattosecond pulses to extract amplitude and phase information for electronic wave functions. We furthermore discuss experiments where ultrashort laser pulses with a reproducible waveform control electron dynamics in the D2+ molecular ion on attosecond timescales. Attosecond sci- ence is coming of age and presently is reaching a level of maturity and sophistication that allows detailed investigations of the role of multielectron dynamics in physics and chemistry. [ABSTRACT FROM AUTHOR]

We present an iterative method for the extraction of velocity and angular distributions from two-dimensional (2D) ion/photoelectron imaging experiments. This method is based on the close relationship which exists between the initial 3D angular and velocity distribution and the measured 2D angular and radial distributions, and gives significantly better results than other inversion procedures which are commonly used today. Particularly, the procedure gets rid of the center-line noise which is one of the main artifacts in many current ion/photoelectron imaging experiments. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The article presents information according to which X-ray techniques can be used to capture the dynamics of electron density in a hydrogen atom and a crystalline powder of potassium dihydrogen phosphate. It mentions that electronic wave functions can be studied by diffraction of an X-ray free electron laser (FEL). It also states that experiments based on X-ray FEL, laser plasmas and high-harmonic generation helps in analyzing the inner dynamics of materials.

Recording molecular movies on ultrafast timescales has been a longstanding goal for unravelling detailed information about molecular dynamics. Here we present the direct experimental recording of very-high-resolution and -fidelity molecular movies over more than one-and-a-half periods of the laser-induced rotational dynamics of carbonylsulfide (OCS) molecules. Utilising the combination of single quantum-state selection and an optimised two-pulse sequence to create a tailored rotational wavepacket, an unprecedented degree of field-free alignment, 〈cos2θ2D〉 = 0.96 (〈cos2θ〉 = 0.94) is achieved, exceeding the theoretical limit for single-pulse alignment. The very rich experimentally observed quantum dynamics is fully recovered by the angular probability distribution obtained from solutions of the time-dependent Schrödinger equation with parameters refined against the experiment. The populations and phases of rotational states in the retrieved time-dependent three-dimensional wavepacket rationalises the observed very high degree of alignment. Molecular movies provide crucial information of fundamental processes like energy and charge transfer, bond breaking etc. Here the authors show the time evolution of the rotational wave packet called the molecular movie of OCS molecules by Coulomb explosion imaging. [ABSTRACT FROM AUTHOR]

We present measurements of photoelectron angular distributions (PADs) for the ionization of aligned CO2 molecules by an extreme ultraviolet laser pulse (17–45 eV) that is produced via high-harmonic generation, and that is polarized perpendicularly to the alignment laser axis. Differential PADs are recorded by taking the difference between two measurements for aligned and anti-aligned molecules. The results are compared with ab initio multi-channel R-matrix calculations, which are extended to include the computation of PADs. The calculations agree very well with the experiment, and are resolved with respect to the internal state of the ion and the polarization of the ionizing laser field relative to the molecular frame. For a sufficiently high, but experimentally achievable degree of alignment, the nodal structure of the molecular orbital becomes visible in the PAD. [ABSTRACT FROM AUTHOR]

We investigate non-adiabatic dynamics of NO molecules that are photo-excited in the vacuum ultraviolet photon energy range using time-resolved velocity map imaging. Highly excited valence and Rydberg states are populated with a tunable (147–151 nm) femtosecond laser pulse and then ionized by a time-delayed near-IR laser pulse. Three main contributions are observed in the photoelectron kinetic spectra with corresponding electron yields that show pronounced oscillations. Two oscillations are assigned to ro-vibronic coupling in the valence-Rydberg mixture of the B and 4dδ N2Δ(v = 0) states and the B2Π(v = 25) and 4pπ K2Π(v = 1) states, respectively. We assign a third oscillation to originate from a coupling between two Rydberg states. [ABSTRACT FROM AUTHOR]