R. R. Lucchese

Bio: R. R. Lucchese is an academic researcher from Texas A&M University. The author has contributed to research in topics: Photoionization & Ionization. The author has an hindex of 15, co-authored 40 publications receiving 685 citations. Previous affiliations of R. R. Lucchese include Tohoku University.

4sigma-1 inner valence photoionization dynamics of NO derived from photoelectron-photoion angular correlations

Abstract: A complete description of the 4sigma photoionization dynamics of NO has been derived from angle resolved photoelectron-photoion-coincidence experiments. The combination of measurements performed with linearly and circularly polarized light has made it possible to obtain a unique set of complex dipole matrix elements. A comparison with multichannel-Schwinger-configuration-interaction calculations shows good agreement in the general shapes of the angular distributions due to the correct description of the main components and phase differences. Still, many transition moments agree only qualitatively.

Intensity dependence of multiple orbital contributions and shape resonance in high-order harmonic generation of aligned N 2 molecules

Abstract: We report measurements and theoretical simulations of high-order harmonic generation (HHG) in aligned N${}_{2}$ molecules using a 1200-nm intense laser field when the generating pulse is perpendicular to the aligning one. With increasing laser intensity, the minimum in the HHG spectra first shifts its position and then disappears. Theoretical simulations including the macroscopic propagation effects in the medium reproduce these observations and the disappearance of the minimum is attributed to the additional contribution of HHG from inner orbitals. We also predict that the well-known shape resonance in the photoionization spectra of N${}_{2}$ should exist in the HHG spectra. It is most clearly seen when the generating laser is parallel to the aligning one and disappears gradually as the angle between the two lasers increases. No clear evidence of this shape resonance has been reported so far when using lasers with different wavelengths. Further experimentation is needed to draw conclusions.

High harmonic spectroscopy of the Cooper minimum in molecules.

Abstract: The Cooper minimum (CM) has been studied using high harmonic generation solely in atoms. Here, we present detailed experimental and theoretical studies on the CM in molecules probed by high harmonic generation using a range of near-infrared light pulses from � ¼ 1:3 to 1:8 � m. We demonstrate the CM to occur in CS2 and CCl4 at � 42 and � 40 eV, respectively, by comparing the high harmonic spectra with the known partial photoionization cross sections of different molecular orbitals, confirmed by theoretical calculations of harmonic spectra. We use CM to probe electron localization in Cl-containing molecules (CCl4, CH2Cl2, and trans-C2H2Cl2) and show that the position of the minimum is influenced by the molecular environment. The electronic structure of atoms and molecules is mainly studied using photoelectron spectroscopy. Photoionization cross sections (PICS) and angular distribution parameters, determined as a function of photon energy, enable us to probe the nature of atomic and molecular orbitals. In atoms, if an orbital has a radial node, the dipole matrix element describing the transition from initial ground state to final continuum state can change sign as a function of photon energy. The PICS undergoes a Cooper minimum (CM) at the photon energy coinciding with the sign change [1]. An analogous effect was also observed in the photoionization of molecules containing atoms that are known to exhibit a CM [2]. High harmonic generation (HHG), in which an electron removed by the incident laser field gains energy from the field and recombines with the parent ion emitting highenergy photons [3], can also be used to probe the structure and dynamics of the recombining system that is encoded in the emitted harmonic spectrum. HHG is a new spectroscopic probe with the potential for angstrom spatial and attosecond temporal resolution, set by the shortest de Broglie wavelength of the recolliding electron and by the subcycle recollision dynamics, respectively. It has been used to image molecular orbitals [4], electronic wave packets [5], and nuclear dynamics [6] in simple aligned molecules as well as to probe collective multielectron dynamics [7] in atoms. The recombination matrixelement inthe HHGprocessis, in essence, the inverse of photoionization, and the CM results in an amplitude modulation of the harmonic spectrum that is independent of both laser wavelength and intensity. To date, high harmonic spectroscopy has only been used to study CMs associated with the electronic structure of noble gases such as Ar [8,9] and Kr [7]. Several recent experimental and numerical studies [10‐12] have focused on the origin of a shift in the position of the CM between photoionization and HHG emission. Whereas high harmonic spectroscopy has been successful in probing atomic and some simple molecular systems, extending this tool to polyatomic molecules has been difficult due to the complex nature of molecular orbitals and multielectron dynamics, thus restricting its viability as a general spectroscopic tool. Since multicenter [13] and multiorbital interferences [14] can also modulate the harmonic spectrum along with the CM, disentangling these effects is challenging in molecules. In this Letter, we show that HHG in randomly oriented molecules containing S and Cl atoms exhibits a CM. We present the first observation of a CM in the harmonic spectrum of CS2 and show that it agrees very well with experimental PICS. Theoretical calculations of PICS and harmonic spectra in CS2 confirm our results. To understand how the atomic nature of a particular molecular orbital influences the photoionization dynamics, we generated high harmonics in CCl4, CH2Cl2, and trans-C2H2Cl2 .I n these molecules, the CM was monitored over a range of wavelengths and intensities that allowed its identification. High harmonics were produced in a finite gas cell of length 10 mm with 0.6 mm apertures. A 30 cm achromatic lens was used to focus 1:3‐1:8 � m near-infrared (NIR) light pulses into the gas cell through a 2 mm thick calcium fluoride window. An optical parametric amplifier pumped by a Ti:sapphire regenerative amplifier (3.5 mJ, 40 fs, 100 Hz, 0:8 � m) produced 80 fs NIR pulses whose energies varied from 0.9 mJ at 1:8 � m to 1.3 mJ at 1:3 � m. The harmonics were dispersed by a flat-field concave grating at grazing incidence onto a microchannel plate detector coupled to a phosphor screen and then imaged by a charge-coupled device camera. The spectrometer was calibrated by measuring the transmitted spectrum after an

Vector correlations in dissociative photoionization of O2 in the 20–28 eV range. II. Polar and azimuthal dependence of the molecular frame photoelectron angular distribution

Abstract: A combined experimental and theoretical study of the polar and azimuthal dependence of the molecular frame photoelectron angular distributions (MFPADs) for inner-valence-shell photoionization of the O2 molecule into the O2+(B 2Σg−,3 2Πu,c 4Σu−) states is reported. The measured MFPADs, for each orientation of the molecular axis with respect to the linear polarization of the synchrotron radiation, are derived from the spatial analysis of the (VO+,Ve,P) vector correlation, where the nascent ion and electron velocity vectors VO+ and Ve are determined for each dissociative photoionization (DPI) event using imaging and time of flight resolved coincidence technique as described in the companion paper of this series [J. Chem. Phys. 114, 6605 (2001)]. Expressed in the general form of four FLN(θe) functions which contain all the dynamical information about the photoionization processes, they are compared with the MFPADs computed using the multichannel Schwinger configuration interaction method. A very satisfactory agreement is found. When the lifetime of the O2+ ionic states is a significant fraction of the rotational period, the rotational motion of the molecule is included in the quantal derivation of the MFPADs. Measured MFPADs are also reported for the additional DPI process identified in Paper I, and for DPI involving the excitation of the neutral (3 2Πu,4sσg) Rydberg state.

Probing molecular frame photoionization via laser generated high-order harmonics from aligned molecules.

Abstract: Present experiments cannot measure molecular frame photoelectron angular distributions (MFPAD) for ionization from the outermost valence orbitals of molecules. We show that the details of MFPAD can be retrieved with high-order harmonics generated by infrared lasers from aligned molecules. Using accurately calculated photoionization transition dipole moments for fixed-in-space molecules, we show that the dependence of the magnitude and phase of the high-order harmonics on the alignment angle of the molecules observed in recent experiments can be quantitatively reproduced. This result provides the needed theoretical basis for ultrafast dynamic chemical imaging using infrared laser pulses.

Attosecond Physics

Abstract: Summary form only given. Fundamental processes in atoms, molecules, as well as condensed matter are triggered or mediated by the motion of electrons inside or between atoms. Electronic dynamics on atomic length scales tends to unfold within tens to thousands of attoseconds (1 attosecond [as] = 10-18 s). Recent breakthroughs in laser science are now opening the door to watching and controlling these hitherto inaccessible microscopic dynamics. The key to accessing the attosecond time domain is the control of the electric field of (visible) light, which varies its strength and direction within less than a femtosecond (1 femtosecond = 1000 attoseconds). Atoms exposed to a few oscillations cycles of intense laser light are able to emit a single extreme ultraviolet (XUV) burst lasting less than one femtosecond. Full control of the evolution of the electromagnetic field in laser pulses comprising a few wave cycles have recently allowed the reproducible generation and measurement of isolated sub-femtosecond XUV pulses, demonstrating the control of microscopic processes (electron motion and photon emission) on an attosecond time scale. These tools have enabled us to visualize the oscillating electric field of visible light with an attosecond "oscilloscope", to control single-electron and probe multi-electron dynamics in atoms, molecules and solids. Recent experiments hold promise for the development of an attosecond X-ray source, which may pave the way towards 4D electron imaging with sub-atomic resolution in space and time.

Recoil-ion and electron momentum spectroscopy: reaction-microscopes

Abstract: Recoil-ion and electron momentum spectroscopy is a rapidly developing technique that allows one to measure the vector momenta of several ions and electrons resulting from atomic or molecular fragmentation. In a unique combination, large solid angles close to 4π and superior momentum resolutions around a few per cent of an atomic unit (a.u.) are typically reached in state-of-the art machines, so-called reaction-microscopes. Evolving from recoil-ion and cold target recoil-ion momentum spectroscopy (COLTRIMS), reaction-microscopes—the `bubble chambers of atomic physics'—mark the decisive step forward to investigate many-particle quantum-dynamics occurring when atomic and molecular systems or even surfaces and solids are exposed to time-dependent external electromagnetic fields. This paper concentrates on just these latest technical developments and on at least four new classes of fragmentation experiments that have emerged within about the last five years. First, multi-dimensional images in momentum space brought unprecedented information on the dynamics of single-photon induced fragmentation of fixed-in-space molecules and on their structure. Second, a break-through in the investigation of high-intensity short-pulse laser induced fragmentation of atoms and molecules has been achieved by using reaction-microscopes. Third, for electron and ion-impact, the investigation of two-electron reactions has matured to a state such that the first fully differential cross sections (FDCSs) are reported. Fourth, comprehensive sets of FDCSs for single ionization of atoms by ion-impact, the most basic atomic fragmentation reaction, brought new insight, a couple of surprises and unexpected challenges to theory at keV to GeV collision energies. In addition, a brief summary on the kinematics is provided at the beginning. Finally, the rich future potential of the method is briefly envisaged.

Photoelectron angular distributions.

Abstract: Angle-resolved photoelectron spectroscopy has been performed for more than 70 years in various guises, but recently its potential to help solve in detail problems in the photoionization dynamics and intramolecular dynamics of gas-phase molecules has been recognized. One key development has been the design of experiments in appropriate geometries to extract information that pertains to the molecular frame, another has been the development of imaging spectrometers, and a third is the use of ultrafast lasers to cause photoionization. In this review, which is aimed at experimentalists, simple expressions for photoelectron angular distributions (PADs) in various experimental geometries are given and their applications explained.

Attosecond Electron Dynamics in Molecules.

Abstract: Advances in attosecond science have led to a wealth of important discoveries in atomic, molecular, and solid-state physics and are progressively directing their footsteps toward problems of chemical interest. Relevant technical achievements in the generation and application of extreme-ultraviolet subfemtosecond pulses, the introduction of experimental techniques able to follow in time the electron dynamics in quantum systems, and the development of sophisticated theoretical methods for the interpretation of the outcomes of such experiments have raised a continuous growing interest in attosecond phenomena, as demonstrated by the vast literature on the subject. In this review, after introducing the physical mechanisms at the basis of attosecond pulse generation and attosecond technology and describing the theoretical tools that complement experimental research in this field, we will concentrate on the application of attosecond methods to the investigation of ultrafast processes in molecules, with emphasis i...

Generalized molecular orbital tomography

Abstract: Atomic and molecular gases generate extreme ultraviolet light when excited by pulses of intense laser light. This emission provides information about the inner workings of the molecules and even enables us to map electron orbitals. However, so far molecular orbital tomography has been restricted to simple molecules. A technique that can be applied to more complicated molecules is now unveiled.