Attosecond Technology Project
Contact: Professor John Tisch
The fundamental processes of chemistry, biology and material science are mediated by electronic and nuclear motions of the constituent atoms. The electronic motions inherent to these systems have attosecond time-scales (1 attosecond = 10-18 sec) which are too fast to resolve with current technology.
This Basic Technology project aims to develop the technological tools to study electron motion in matter with both attosecond time-scale resolution and sub-Ångstrom spatial resolution. Underpinned by extreme-ultraviolet (EUV) light sources producing attosecond duration light pulses, these tools open the door not only for real-time observation but also time-domain control of electron dynamics on the atomic scale.
This project represents a set of front-line technological challenges in laser engineering, optical pulse diagnostics, extreme ultraviolet optics, molecular physics and energy/momentum resolved electron detection.
Our team comprising scientists from Imperial College London, University College London, the universities of Oxford, Reading Birmingham, and the Rutherford Appleton Laboratory (CCLRC) has brought together a range of expertise to tackle these challenges. As we have developed the technology, new science has followed, for example we have made the fastest ever measurement of molecular dynamics. The project has also succeeded in training more than a dozen doctoral students and fostering a new UK attosecond science community. It has also transferring new technology to the UK science base thereby increasing both the expertise and the capacity to do attosecond science in the UK.
Further information can be found on the Attosecond Technology Project website
Ultrafast Quantum Control
The work on ultrafast quantum control goes hand-in-hand with our research into making ultrafast measurements in the attosecond domain. We continue to look beyond attosecond/femtosecond probing of ultrafast processes to using the same exquisitely controlled fields also to control these processes.
Two examples have been explored over the last year in the laboratory. We have proven how a two-colour strong field synthesized from the orthogonally polarized laser fundamental and its second harmonic can be used to control the intensity in high harmonic generation with an amplitude modulation depth that varies by nearly two orders of magnitude as the relative phases of the fields are changed. Moreover we have shown and explained how the quantum path (short or long trajectory) that dominates in the HHG emission is highly sensitive to the relative phase, allowing a new approach to adjusting the return time in HHG and so providing an additional handle in attosecomd measurement. In a second example we have demonstrated how we can achieve very high degrees of molecular alignment in an impulsive laser alignment scheme through the enhanced cooling achieved by mixing with an appropriate buffer gas. Detailed measurements that fit the roational revival to a calculation have allowed us to make accurate retrieval of the rotational temperature of the molecules.
There are a number of theoretical studies of various aspects of quantum control going on in parallel with our experimental work.
Theory of ultrafast many-electron processes in atoms, molecules and cluster
Attosecond laser technology allows us to resolve in time the correlated dynamics of electrons in atoms, molecules and clusters. Being typically the system's response to photoionisation or photoexcitation, this dynamics can proceed via a variety of processes in which the electrons exchange energy with each other and with the external field. While some of these processes (such as Auger effect) are very well known, some others (such as inter-atomic decay and its variants) have been discovered relatively recently or, perhaps, are yet to be discovered. Our main goal as theorists is to predict and to model the new laser-induced many-electron transitions as well as to propose schemes by which one could characterise these phenomena experimentally using the techniques of attosecond laser science. We are also interested in devising schemes for control of many-electron dynamics with laser fields. In our work, we use a combinaiton of the theoretical tools of strong field laser physics and first-principles electron structure theory to take into account both the electron interaction with the laser field and the electronic correlation. We work in close interaction with the experimentalists of the laser consortium and with other theoretical groups in the UK, Germany, Italy and Czech Republic.
High Power Lasers and High Energy Density Plasmas
Contact: Professor Rolan d Smith
High-power short-pulse lasers all ow us to d eliver peak opti cal powe rs of many Te rrawatts, and couple large amounts of energy into matter on timescales less than a picosecond. As a result we can heat a nd compress material to the extreme condit ions found within planetary cores, stars, or even more exotic locations such as supernova remnants and plasma jets launched from the accretion disk surrounding a black hole. In this way lasers can be used to conduct “laboratory astrophysics ” ex periments whi ch incorporat e the same key pr o cesses that govern the behaviour of large-scale astrophysical object. By casting the theoretical descriptions of these systems in terms of dimensionless parameters (e.g. the Mach number, the ratio of the speed of an object to the sound speed) we can make detailed comparisons between laboratory events that evolve over nanosecond time and millimetre length scales with those occurring naturally over light year distances and millennia of time.
To underpin this work we are building a new high-energy, multi-beam laser system called Cerberus in collaboration with the Plasma Physics group. Once completed it will be the largest University based laser system in the UK. One of the key aims of this project is to combine the ability of the laser to create and probe matter on sub-picosecond timescales with the capability of the Magpie Z-Pinch, the worlds largest non-military pulsed power machine. Magpie is a uniquely capable device for creating plasmas in which magnetic fields dominate the flow of hot, dense matter of the kind found in the jets launched by young stellar objects. The Cerberus laser can be used to accurately probe plasma properties including density, temperature and flow. In the near future we plan to use a high intensity, sub-picosecond beam from Cerberus interacting with a thin metal foil to launch multi-megavolt proton beams. This will allow us to image the details of the complex 3-dimensional electric and magnetic field structures within plasma jets launched by Magpie for the first time.