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Strathclyde Intense Laser Interaction Studies (SILIS) group

We have a new vibrant research programme which is based on lasers, plasmas and electron beams. It is yielding exciting new results, some of which may have important industrial applications. This all comes out of having a creative group of scientists with unique tools that are focusing on new phenomena resulting from extreme states of matter created at the focus of high power lasers. For more information on potential PhD projects please contact Prof. Dino Jaroszynski at dino-at-phys.strath.ac.uk*.
*Please replace -at- with @. This is present for spam prevention.

Developments of high-power femtosecond lasers have given rise to a whole new branch of research where extreme intensities produce extreme states of matter which are accompanied by the emission of high energy particles and hard x-ray photons. At these intensities matter is fully ionised and exists as plasma where charge particles can be accelerated to highly relativistic velocities by electrostatic forces and light pressures. These forces can be harnessed to produce compact new sources of coherent and incoherent electromagnetic radiation and energetic particles, which can mimic astrophysical conditions. Indeed, a new area of laboratory scale astrophysics has sprung up around table-top terawatt femtosecond lasers.

The group at Strathclyde carries out research in several areas covering the basic physics of the interaction of electromagnetic radiation with plasma, of fundamental interest, to the more applied physics of femtosecond laser micromachining, of significant industrial relevance. The group, which currently consists of 6 academic and research staff members (+ 2 more in March 2003), technicians and students, undertakes several projects using both experimental and theoretical methods. They lead a large Basic Technology consortium, consisting of seven UK research establishments (Oxford University, Imperial, Rutherford Appleton Laboratory, Daresbury Laboratory, St Andrews University and University of Abertay Dundee), and several EU, Russian and US collaborators, to develop laser-wakefield accelerators and utilise the high-energy electrons beam in a free-electron laser to produce a coherent radiation source for time-resolved studies. Demonstration of the complete system will be made at Strathclyde and could revolutionise the way science is done by providing a future compact ultra-short pulse x-ray source. In addition to laser wakefield accelerator development the group also investigates non-linear optics of laser-plasma interactions and the basic physics of laser-cluster interactions. Many of these studies investigate the interaction of lasers with plasma as potential electromagnetic sources from terahertz frequencies to the hard x-rays. The experimental workhorse for the group’s studies is a collection of synchronised Ti:sapphire femtosecond lasers producing up to several terawatts at the TOPS facility at Strathclyde, which is currently being augmented by a 10 MeV accelerator. The group also carry out collaborative research at other facilities in the UK and abroad.

Projects

  1. Clusters Exposed to Intense Laser Fields: Efficient X-ray and XUV Radiators
  2. Laser-Plasma Interactions
  3. Non-Linear Optics in Plasmas
  4. Energy Transfer between Radiation and Particles
  5. Free-Electron Laser Research
  6. Laser Induced Nuclear Phenomena
  7. Ion acceleration driven by high intensity laser-solid interactions

Clusters Exposed to Intense Laser Fields: Efficient X-ray and XUV Radiators

Intense laser heated matter in the form of high-density gas jets, solids, and noble gas clusters emit high peak brightness x-rays and particles with energy up to several MeV and their inherent synchronization with the laser source is ideal for time-resolved diffraction, imaging and other pump-probe studies on femtosecond time scales. Radiative emission can be incoherent (eg. inner shell transitions of ions, bremsstrahlung emission) and coherent (high order harmonics – up to 300th of 800 nm). High-density gas jets and gas filled capillaries are efficient sources of high harmonics and soft x-ray lasing when subject to ultra-short laser pulses. Intense laser heating of solids forms plasma with densities and temperatures that are usually found only in astrophysical conditions here they radiate large flux of line and continuum x-rays with tens of keV photon energies. Clusters of noble gases, on the other hand, provide a debris-free source with excellent yield in the x-ray region of the spectrum.

Atomic clusters (nanometers diameter balls consisting of > 1 million weakly bound atoms) irradiated by intense, femtosecond laser pulses undergo instantaneous ionisation and create a nano-plasma of extremely high temperature and pressure. This creates highly ionised species through collisions and is followed by a rapid expansion. Large x-ray flux is measured from such high-density plasmas including krypton K(alpha) emission at 12.6 keV as part of an ongoing project at TOPS. This remains the highest energy x-rays reported so far from noble gas clusters and further studies have to be carried out to produce even shorter wavelength x-rays meeting further demands on material analysis. Owing to high local densities in clusters, the high harmonic yield also can potentially be enhanced and various electron-ion re-scattering mechanisms can be investigated.

The main objective of the project will be to theoretically and experimentally investigate the ultra-short laser-cluster interaction processes, and to optimise x-ray and xuv emissions (coherent and incoherent) at relativistic and sub-relativistic laser intensities. The hardware available in the laboratories includes 5TW (800 nm, 50 fs) laser, dedicated vacuum chambers, x-ray (1 - 150 keV) and xuv (5 - 100 nm) spectrometers. The project will is an extension of ongoing research at TOPS.

Laser-Plasma Interactions

The subject of the research will be an experimental and/or theoretical and numerical investigation of high-power laser-matter interaction. Advances in short-pulse laser technology have made it possible to produce multi-terawatt pico-and femtosecond laser pulses which can be focused to extremely high on-target intensities - beyond 10^20 W/cm^2. The study of the interaction of these intense laser pulses with plasmas, clusters and gases is relevant to several applications including collective charged particle acceleration and the generation of intense hard X-ray radiation. From the calculational point of view, the subject of this project lies in the forefront of modern theoretical physics. The techniques involved range from simplified weakly nonlinear 1-D models to fully relativistic 3-D particle-in-cell numerical codes.

The experimental studies involve the use of terawatt lasers at TOPS and RAL and the implementation of several advanced optical and electron beam diagnostic techniques and the development of plasma channel waveguides A state-of-the-art 10 MeV photoinjector accelerator is being developed as an injector for the laser-wakefield accelerator. These accelerators are also being used as a test-bed for developing advanced free-electron lasers at Strathclyde and for developing intense terahertz sources for time-resolved studies.

Non-Linear Optics in Plasmas

The dependence of the refractive properties of plasma on electron density, which may be modulated by intense electromagnetic radiation, makes it a non-linear optical medium, with interesting phenomena like, e.g., four-wave mixing or Raman amplification.

Energy Transfer between Radiation and Particles

A short intense electromagnetic pulse in plasma leaves behind a wake of density modulations and longitudinal electric field, which may be used to accelerate electrons (and ions). On the other hand, a beam of energetic electrons can emit coherent radiation if they are forced to oscillate transversely (free-electron laser). TOPS is the lead partner in a Basic Technology project to investigate the combination of these principles to develop a coherent radiation source for time-resolved studies.

Free-Electron Laser Research

Another example of new work that has come out of our research programme at Strathclyde is the demonstration of superradiance in the free-electron laser. This work is pointing the way forward to producing ultra-short pulses from the free-electron laser. This is very relevant to the production of ultra-bright attosecond x-ray pulses in future x-ray free-electron lasers. These ideas are being developed in the Basic Technology project and if successful, there will be an opportunity for scientists to make x-ray videos of atomic and molecular motion with unprecedented time resolution.

Laser Induced Nuclear Phenomena

Supervisor: K. Ledingham

When very intense lasers are focused on to solids or gases as shown above, very energetic beams of electrons, protons or neutrons are produced. These can be used to produce radio-active sources in a similar way to reactors and accelerators but without the large radiation hazard and on a very much reduced physical size. The Strathclyde group is using this exciting new technology for fundamental studies in nuclear and particle physics as well as medical production of isotopes and developing proton beams for proton oncology. There are a number of different projects in this area using the world’s most powerful laser at the Rutherford Appleton Laboratory and other European High Intensity Laser Systems.

Other very interesting projects using the TOPS laser facilities at Strathclyde involve the detection of environmentally hazardous molecules like explosives, drugs and bio-molecules. For further details please contact Prof. Ken Ledingham at
k.ledingham-at-phys.strath.ac.uk*.
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Ion acceleration driven by high intensity laser-solid interactions

A PhD studentship is available in a group investigating the interaction of  intense laser pulses with plasma, under the supervision of Dr. Paul McKenna, at the University of Strathclyde. An experimental PhD project is available to investigate laser driven MeV ion acceleration. The properties of laser-accelerated ion beams are  fundamentally different from beams available via conventional acceleration techniques and open up the possibility of innovative applications, mainly related to the ultrashort duration of the particle bursts. The project will aim to optimise ion production from laser pulse interactions with a range of targets. The studentship is funded as part of a challenging new project (the LIBRA Basic Technology project) involving a consortium of eight UK institutions. The research will be carried out using high power
lasers at the University of Strathclyde, the Rutherford Appleton Laboratory and a number of EU facilities.

For further information on the PhD project contact Dr. Paul McKenna. For information about PhD study in the Physics Department at the University of Strathclyde, and for an online application form go to the postgraduate page.

Funding Notes

The project is suitable for candidates from within the EU who have, or expect to obtain, at least a 2:1-class degree (or equivalent) in physics.

Recent example group publications related to the project:

  1. P McKenna et al., "Lateral electron transport in high intensity laser-irradiated foils diagnosed by ion emission", Physical Review Letters, 98, Art. No. 145001 (2007).
  2. P McKenna et al., "Low- and medium-mass ion acceleration driven by petawatt laser plasma interactions", Plasma Physics and Controlled Fusion, 49, B223-B231 (2007)
  3. L Robson et al., "Scaling of proton acceleration driven by petawatt laser-plasma interactions", Nature Physics, 3, 58-62 (2007).
  4. D C Carroll et al., "Active manipulation of the spatial energy distribution of laser accelerated proton beams", Physical Review E, 76, Art. No. 065401 (2007).