Attoseconds (10^(-18) sec) are the natural time-scale for multi-electron effects during complete ionization and break-up of multi-electron atoms and molecules. The recent advances in generating ultrashort laser pulses raise the possibility to investigate atomic, molecular, and nuclear physics at this new time-scale, bringing a revolution in our microscopic knowledge and understanding of matter. Two fascinating and complementary challenges of Attoscience are to identify the physical mechanisms underlying the correlated multi-electron dynamics--of fundamental interest to, for instance, molecular imaging--in atomic and molecular systems and to devise schemes to probe/control these mechanisms. This is the overall aim of the proposed research. Steering the electronic motion for manipulating small molecules will pave the way for modifying the structure of complex biomolecules, thus impacting such diverse fields as physics, chemistry, biology and material science. The problem consists of exploring the interaction of complex atoms and molecules driven by intense and ultrashort laser pulses. Given the state of the art in computational capabilities, solving this problem with three-dimensional (3-d) first-principle techniques, namely, quantum mechanical ones, is an immense task. Thus, classical/semiclassical techniques, which are much faster than quantum mechanical ones, will be instrumental in exploring the correlated electron dynamics in driven complex atomic and molecular systems. I recently developed, in the context of the driven double ionization of Helium, a 3-d classical method that addresses the full fragmentation of driven systems. The advantage of this technique is that it is much faster than quantum mechanical treatments and it accounts for the Coulomb singularity--the infinitely strong force an electron experiences when it is close to the atomic center. It is thus a step forward compared to previous classical studies which ignore the Coulomb singularity altogether. I propose to generalize this quasiclassical technique, and develop an efficient and sophisticated numerical tool for the treatmentof the full fragmentation of complex driven atomic and molecular systems.Using this 3-d quasiclassical technique, I will first address multi-electron effects in three electron atoms driven by strong laser pulses--a problem vastly unexplored. One of the main goals is to probe (time-resolve) the main mechanisms/paths the three electrons follow to escape during the fragmentation process when the atom is interacting with a very weak field (single photon absorption). I will do so using a circularly polarized infrared ultrashort laser pulse as an attosecond clock to map the information obtained from the observed spectra of the final fragments to the attosecond correlated electron dynamics. I will then proceed to explore the correlated electron dynamics in the double ionization of two- active or two-electron diatomic molecules with moving nuclei when driven by intense ultrashort laser pulses. This problem is at the forefront of Attoscience and is far from being theoretically well understood. Using pulses of different intensity I will be able to explore different ionization regimes and for each regime explore the different mechanisms that govern the two electron escape, the effect of the two atomic centers on the double ionization, and the interplay of processes that result in different final products. The vision is to generalize these studies to tackle driven triatomic molecules with moving nuclei--an unexplored problem--and study the break-up geometries and their dependence on the initial molecular state. Finally, combining my expertise on probing single photon processes and on multi-electron effects of strongly driven molecules, I will address time-resolving and controlling the electronic motion during the break-up of driven multi-center molecules using combinations of ultrashort laser pulses.

The ability to control the evolution of a reaction is a long-standing goal of chemistry. One approach is to use the electric field provided by a laser pulse as the guide. Recent work has focused on shaping and timing the pulse so that the field interacts with the molecules in a particular way to influence the energy flow through the molecule and thus eventually the course of a reaction. The optimal pulse shape is achieved by using a feedback loop , focusing on a signal related to the desired outcome and allowing a computer algorithm to change the pulse shape during repeated cycles of the experiment until the signal is maximised. This optimal control scheme has proved to be able to control a wide range of chemical systems, but the complicated pulse shapes provide little insight into the procedure, and the experiments have a black box nature. A different, very appealing, approach to control through a laser field is to use the field to change the shape of the potential energy surface over which the reaction proceeds. This can be acheived using a strong pulse which induces Stark shifting of the surface. By careful timing of a pulse of the appropriate strength, it has been shown that it is possible to control the products from IBr dissociation by effectively changing the barrier height to the different possible channels.The project aims to investigate theoretically this potentially general approach to laser control. The results should start to build up a picture of how the complicated potential energy surfaces of small molecules are altered by interaction with the field. This will help in the development of experiments and in our understanding of how molecules behave in a light field.

Ultra-short and ultra-intense laser pulses provide an impressive camera into the world of electron motion. Attoseconds and sub-femtoseconds are the natural time scale of multi-electron dynamics during the ionization and break-up of atoms and molecules. The overall aim of the proposed work is to investigate attosecond phenomena, pathways of correlated electron dynamics and effects due to the magnetic field of light in three and four-electron ionization in atoms and molecules triggered by intense near-infrared and mid-infrared laser pulses. Correlated electron dynamics is of fundamental interest to attosecond technology. For instance, an electron extracted from an atom or molecule carries information for probing the spatio-temporal properties of an ionic system with angstrom resolution and attosecond precision paving the way for holography with photoelectrons. Moreover, studies of effects due to the magnetic field of light in correlated multi-electron processes are crucial for understanding a variety of chemical and biological processes, such as the response of driven chiral molecules. Chiral molecules are not superimposable to their mirror image and are of particular interest, since they are abundant in nature. The proposed research will explore highly challenging ultra-fast phenomena involving three and four-electron dynamics and effects due to the magnetic field of light in driven atoms and during the break-up of driven two and three-center molecules. We will investigate the physical mechanisms that underly these phenomena and devise schemes to probe and control them. Exploring these ultra-fast phenomena constitutes a scientific frontier due to the fast advances in attosecond technology. These fundamental processes are largely unexplored since most theoretical studies are developed in a framework that does not account for the magnetic field of light. Moreover, correlated three and four-electron escape is currently beyond the reach of quantum mechanical techniques. Hence, new theoretical tools are urgently needed to address the challenges facing attoscience. In response to this quest, we will develop novel, efficient and cutting-edge semi-classical methods that are much faster than quantum-mechanical ones, allow for significant insights into the physical mechanisms, compliment experimental results and predict novel ultra-fast phenomena. These semi-classical techniques are appropriate for ionization processes through long-range Coulomb forces. Using these techniques, we will address some of the most fundamental problems facing attoscience. Our objectives are: 1) Identify and time-resolve novel pathways of correlated three-electron dynamics in atoms driven by near-infrared and mid-infrared laser pulses. 2) Explore effects due to the magnetic field of light in correlated two and three-electron escape during ionization in atoms as well as in two and three-center molecules driven by near-infrared and mid-infrared laser pulses that are either linearly or elliptically polarized or by vector beams, i.e. "twisted" laser fields, an intriguing form of light that twists like a helical corkscrew. 3) Control correlated multi-electron ionization and the formation of highly exited Rydberg states in four-active-electron three-center molecules by employing two-color laser fields or vector beams.

The vision for this research is to develop a novel toolset for flight simulation fidelity enhancement. This represents a step-change in simulator qualification, is well-timed making a significant contribution to the UoL initiated NATO STO AVT-296-RTG activity and will have an immediate impact through engagement with Industry partners. High fidelity modelling and simulation are prerequisites for ensuring confidence in decision making during aircraft design and development, including performance and handling qualities estimation, control law development, aircraft dynamic loads analysis, and the creation of a realistic piloted simulation environment. The ability to evaluate/optimise concepts with high confidence and stimulate realistic pilot behaviour are the kernels of quality flight simulation, in which pilots can train to operate aircraft proficiently and safely and industry can design with lower risk. Regulatory standards such as CS-FSTD(H) and FAA AC120-63 describe the certification criteria and procedures for rotorcraft flight training simulators. These documents detail the component fidelity required to achieve "fitness for purpose", with criteria based on "tolerances", defined as acceptable differences between simulation and flight, typically +/- 10% for the flight model. However, these have not been updated for several decades, while on the military side, the related practices in NATO nations are not harmonised and have often been developed for specific applications. Methods to update the models for improved fidelity are mostly ad-hoc and, without a strong scientific foundation, are often not physics-based. This research will provide a framework for such harmonisation removing the barriers to adopting physics-based flight modelling and will create new, more informed, standards. In this research two aspects of fidelity will be tackled, predictive fidelity (the metrics and tolerances in the standards) and perceptual fidelity (pilot opinion). The predictive fidelity aspect of the research will use System Identification techniques to provide a systematic framework for 'enhancing' a physics-based simulation model. The perceptual fidelity research will develop a rational, novel process for task-specific motion tuning together with a robust methodology for capturing pilots' subjective assessment of the overall fidelity of a simulator. Extensive use will be made of flight simulation and real-world flight tests throughout this project in both the predictive and perceptual fidelity research.