The development of high-intensity lasers will be described, including of the Vulcan Petawatt system which is currently the highest power system world-wide. The possibilities of producing even higher intensities will be discussed.  

Speaker suggested by Dino Jaroszynski

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For further information contact Prof. Gian-Luca Oppo 

(0141-548-3761 or 0141-548-3364) or email to

gianluca@phys.strath.ac.uk  

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PAST EVENTS OF THE ACADEMIC YEAR 2002/2003

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30 October 2002

Structure and behaviour of proteins, nucleic acids and viruses from Raman optical activity.

Prof. Laurence Barron, Department of Chemistry, University of Glasgow

Work in our Glasgow laboratory has demonstrated that Raman optical activity (ROA), which measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light, is a powerful technique for studying solution structure and behaviour of biomolecules [1]. ROA is more incisive than conventional Raman because the largest ROA signals are associated with vibrational coordinates which sample the most rigid and chiral parts of the structure. In proteins, for example, these are usually within the peptide backbone and give rise to ROA band patterns characteristic of the backbone conformation, unlike the parent Raman spectra in which many bands from the sidechains often obscure the peptide backbone bands. Nucleic acid ROA spectra contain information on base stacking, the mutual orientation of sugar and base rings, and the sugar-phosphate backbone conformations. It is also possible to measure ROA spectra of most intact viruses, which contain among other things information about the folds of the major coat proteins and the nucleic acid structure [2].

Protein ROA spectra contain bands from loops and turns in addition to bands from secondary structure and so provide information about the tertiary fold. The large number of structure-sensitive bands makes protein ROA spectra ideal for the application of pattern recognition methods such as principal component analysis (PCA). PCA scatter plots reveal tight clustering of proteins according to fold type and suggest that PCA will enable structural similarites between proteins of unknown structure with those of known structure to be identified in unprecedented detail. ROA is also valuable in studies of unfolded and partially folded proteins, providing new insight into the complexity of order in denatured proteins and the structure and behaviour of proteins involved in the misfolding diseases [3].

A new design of ROA instrument [4], soon to be available commercially from BioTools, should facilitate the widespread use of ROA in biomedical science. Since many gene sequences code for natively unfolded proteins in addition to those coding for proteins with well-defined tertiary folds, both of which are equally accessible to ROA measurements, ROA should be especially valuable in structural genomics.

1. L. D. Barron, L. Hecht, E. W. Blanch and A. F. Bell (2000). Prog. Biophys. Mol. Biol. 73, 1.
2. E. W. Blanch, L. Hecht, C. D. Syme, V. Volpetti, G. P. Lomonossoff, K. Nielsen and L. D. Barron. J. Gen. Virol. 83, 2593.
3. L. D. Barron, E. W. Blanch and L. Hecht (2002). Adv. Prot. Chem. In press.
4. W. Hug and G. Hangartner (1999). J. Raman Spectrosc. 30, 841.  

Speaker suggested by Klaas Wynne

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6 November 2002

Terahertz Photonics

Prof. Dan Mittleman, Rice University, Texas, U.S.A.

Traditionally, the region of the spectrum between 100 gigahertz and 10 terahertz (corresponding to the wavelength range 30 microns - 3 mm) has been among the least explored, due in part to the difficulties associated with efficient generation and detection schemes. However, the recent development of a number of new experimental techniques has sparked a growing interest in the use of terahertz radiation for imaging, spectroscopy, and a variety of commercial applications.

This talk presents an overview of this rapidly developing field, and a description of a few of the unique imaging capabilities of the "T-ray" imaging system. For example, by combining interferometry with the coherent detection capability of time-domain spectroscopy, it is possible to form time-of-flight images with a depth resolution well below the limit imposed by the coherence length of the radiation. The use of broadband radiation for imaging also requires a rethinking of such concepts as the Fresnel zone, which is typically defined only at a single frequency. Such considerations have a bearing on the lateral resolution in a tomographic image, and have implications in fields as diverse as biomedical imaging and geophysical prospecting.  

Speaker suggested by Martin Dawson

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PLEASE NOTE DIFFERENT DAY AND TIME

Monday 11 November 2002, 12:00 (Noon), Room 3.14 John Anderson Building

UNDERSTANDING OR MEMORIZATION: ARE WE TEACHING THE RIGHT THING?

Prof. Eric Mazur, Harvard Univeristy, Massachussets, U.S.A.

Alternative title: Why waste time? Turn your lectures into discussions!

Education is more than just transfer of information, yet that is what is mostly done in large introductory courses -- instructors present material (even though this material might be readily available in printed form) and for students the main purpose of lectures is to take down as many notes as they can. Few students have the ability, motivation, and discipline to synthesize all the information delivered to them. Yet synthesis is perhaps the most important -- and most elusive -- aspect of education. Students get frustrated because they are unable to grasp simple concepts. Instructors get frustrated because they don't know how to help their students grasp the material.

The problem has a relatively simple solution: shift the focus in lectures from delivering information to synthesizing information. This requires students to take more responsibility for obtaining the information in the first place, but this is a process that they are quite good at anyway. With examples from my own discipline (physics), I will illustrate how I discovered rampant problems in my own lectures and how I have begun to remedy the problem.  

Speaker suggested by Allister Ferguson

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PLEASE NOTE DIFFERENT DAY AND TIME

Friday 15 November 2002, 2:00 PM, Room 3.14 John Anderson Building

Supercontinuum generation in photonic crystal fibers

Prof. John Harvey, Physics Department, University of Auckland, New Zealand

Photonic crystal fibres with their high nonlinearity and adjustable group velocity dispersion characteristics provide an ideal medium for the generation of an octave spanning supercontinuum, yielding new insights into the generation mechanisms of the white light. The dominance of Four Wave Mixing effects in specially designed fibres has also enabled the development of a fibre Optical Parameteric Oscillator operating in the visible region.  

Speaker suggested by Willie Firth

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27 November 2002

Lasers for Gas Detection in Environmental Monitoring, Oil Prospection and Disease Diagnosis.

Prof. Miles Padgett, Department of Physics, University of Glasgow

Governments and the public at large are becoming ever more concerned to the gases in our atmosphere and terms such as "green house" gases are now in common usage. Optics offers an alternative approach to the detection and monitoring of many gases. Within the optics Group at Glasgow we have developed a number of optical techniques which have been applied to gas detection in differing applications. The projects I shall cover in this talk are:

Commercialisation of FTUV Gas Detection
Laser Pointer for Gas Safety
Gas Detection for Oil Prospection
Gas Detection for Disease Diagnosis
Gas Monitoring of Volcano Emissions

Representing a mix of commercial and academic research, the talk aims to illustrate that Physics in general and Optics in particular can hold the solution to many problems in diverse fields.  

Speaker suggested by Geoff Duxbury

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11 December 2002

Liquid Helium, Superfluidity, and the Dawn of Time

Prof. Peter McClintock, Department of Physics, University of Lancaster

The symmetry-breaking phase transition that is believed to have occurred ~10^-35 seconds after the dawn of time at the Big Bang would appear to lie forever beyond the reach of experiment -- which is unfortunate given that topological defects in space-time created during this transition may have contributed to the primordial density inhomogeneities that later gave rise to galaxy formation. Arguably, however, the physics of this remote event can be investigated in the laboratory through studies of mathematically analogous but more accessible phase transitions, e.g. the lambda (superfluid) phase transition of liquid ⁴He.

Quite generally, when a physical system passes rapidly through a 2nd order (continuous) phase transition, the creation of topological defects is to be anticipated [1] at a density that depends on the speed with which the transition is traversed [2]. This Kibble-Zurek (K-Z) mechanism is of particular interest in relation to the cosmological phase transition. Just after the transition, at a critical temperaure of ~10²⁷ K, the nascent new phase of the vacuum would have been disordered and must have given rise to a variety of topological defects, including cosmic strings.

Model systems used to study the K-Z mechanism have included liquid crystals, liquid ⁴He [3,4], liquid ³He, and Josephson tunnel junctions. Most of the experiments apparently produce results consistent with the K-Z predictions -- but, mysteriously, not (so far) liquid ⁴He which was the subject of Zurek's original [2] proposal for a cosmological experiment. Superfluid ⁴He is described by a complex macroscopic order parameter (condensate wave function) whose real and imaginary parts play the role of Higgs fields.

The talk will introduce helium and its superfluidity, outline the cosmological scenario, describe and discuss the results of recent ``cosmological experiments'', and consider possible reasons for an unexpectedly null result [4].

[1] T W B Kibble, J. Phys. A, 9, 1387 (1976).
[2] W H Zurek, Nature 317, 505 (1985).
[3] P C Hendry, N S Lawson, R A M Lee, P V E McClintock and C D H Williams, Nature 368, 315 (1994).
[4] M E Dodd, P C Hendry, N S Lawson, P V E McClintock and C D H Williams, Phys. Rev. Lett. 81, 3703 (1998).  

Speaker suggested by Gordon Donaldson and Gian-Luca Oppo

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22 January 2003

Advanced Accelerators and their Role in Modern Radiation Sources

Dr. Mike Poole, ASTeC - Accelerator Science and Technology Centre, CLRC Daresbury Laboratory

Conversion of energy from an electron beam into an output radiation emission is a well established branch of science and technology, ranging from small portable electron tube devices through to the large scale synchrotron light source facilities that are now operated on a national scale. The subject of this talk will be the latest developments of such major facilities and will be restricted to the application of relativistic electron beams.

After reviewing the significant properties of such radiation sources the initial part of the talk will concentrate on the design of Synchrotrons configured as electron storage rings and especially on their evolution to the latest ultra-high brightness versions. The use of novel magnetic structures called Undulators to generate radiation with a variety of attractive properties will be discussed, including some practical examples. The UK DIAMOND project currently under construction will be used as illustration of such an advanced accelerator and radiation source.

The next major topic will be the Free Electron Laser (FEL) and its operating principles will be explained. Current achievements in delivering radiation in the range from infra-red to extreme ultra-violet output, based on both advanced linear (linac) and circular accelerators, will be reviewed and the limitations discussed. Emphasis will be given to the major role of European projects.

Finally an exciting new development that could revolutionise such national radiation sources will be described. This employs an Energy Recovery Linac (ERL) instead of a storage ring and the advantages of this choice will be explained. In the proposed Daresbury 4GLS project such an ERL will deliver exceptional beam properties leading to a uniquely flexible new national source. In addition to a suite of undulators delivering essentially incoherent but extremely high brightness output, there will be several FELs employing both oscillator and single pass amplifier configurations.  

Speaker suggested by Brian McNeil

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5 February 2003

Fluorescence as a probe of Photosynthesis

Prof. Hilary Evans, Biomolecular Sciences, Liverpool John Moores University

Light energy absorbed by photosynthetic pigments may be used to drive the processes that ultimately end in the fixation of carbon dioxide and nitrogen, or lost as heat or fluorescence. This fluorescence may be used to monitor energy transfer between pigments, electron transfer, and slower enzyme reactions occurring in the overall photosynthetic process.

The lecture will discuss how time resolved fluorescence decays, coupled with fast absorption measurements, can give information about early photosynthetic events, together with the use of fluorescence spectra to fingerprint pigment-protein complexes. Application of such measurements to intact algae and leaves will indicate novel approaches to monitoring the effects of pollution.  

Speaker suggested by Kevin O'Donnell

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19 February 2003

Coulomb Correlations in Semiconductor Heterostructures

Dr. Ian Galbraith, School of Engineering & Physical Sciences, Heriot-Watt University, Edinburgh

The fundamental absorption edge in most semiconductors is dominated by excitonic features, reflecting the existence of bound states of the electron and hole. These are the simplest manifestation of Coulomb correlations in the electron-hole plasma. Higher order correlations are responsible for trions, biexcitons, and ultimately screening. In this talk I will give an overview of recent progress in understanding such correlations from both an experimental and theoretical perspective.  

Speaker suggested by Dino Jaroszynski

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5 March 2003

Electron Transfer Reactions in DNA

Dr. Gavin Reid, Department of Chemistry, University of Leeds

Self-assembling DNA structures look to have a promising future in nanoscale molecular electronics. However, there remains strong disagreement in both the chemistry and physics communities as to whether DNA can ever be an efficient conductor of electricity. Such a fundamental dispute requires new experimental data. This talk will concentrate on femtosecond electron transfer reactions in DNA hosts and will discuss which pathways promote efficient electron transfer reactions and which present significant obstacles.  

Speaker suggested by Klaas Wynne

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19 March 2003

Seeing the particles beneath the waves
Beyond mean field physics with Bose-Einstein condensates in optical lattices

Dr. Immanuel Bloch, Max Planck Institute for Quantum Optics, Garching, Germany

At the heart of a Bose-Einstein condensate lies its description as a single giant matter wave. Such a Bose-Einstein condensate represents the most "classical" form of a matter wave, just as an optical laser emits the most classical form of an electromagnetic wave. Beneath this giant matter wave, however, the discrete atoms represent a crucial granularity, i.e. a quantization of this matter wave field, which has been inaccessible to experiments with Bose-Einstein condensates up to now. I will report on several of our most recent experiments carried out with Bose-Einstein condensates in three-dimensional optical lattices, where this matter wave quantization leads to dramatic effects in the behaviour of the many-body system. For example by controlling the potential depth of the optical lattice we are able to induce a quantum phase transition from a superfluid to a Mott insulating state, which is dominated by strong correlations between the atoms. Furthermore we show that cold collisions between the atoms lead to a periodic collapse and revival of the macroscopic matter wave field of a BEC, which cannot be explained by any of the theories for a weakly interacting Bose gas. In our most recent experiments we have been able to completely control the collisions between atoms on different lattice site. I will show how such unprecedented control can lead to highly entangled many-body states, which could be useful for quantum computation or the simulation of complex many-body Hamiltonians.  

Speaker suggested by Erling Riis

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LEOS DISTINGUISHED LECTURER

26 March 2003

From femtoseconds to attoseconds
Coulomb explosions to dielectric modification

Dr. Paul Corkum, Steacie Institute for Molecular Science, NRC, Canada

Abstract not available.  

Speaker suggested by Martin Dawson

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PLEASE NOTE DIFFERENT LOCATION

2 April 2003, Colville Building Room 4.20

Hydrogen - a doping element in semiconductors ?

Prof. H. Neumann, Department of Physics, Leipzig University, Germany

Incorporation of hydrogen in semiconductors is a subject of scientific and, in particular, of practical relevance which has received a great deal of attention during the last two decades. Hydrogen can be i ncorporated into semiconductors during growth by metalorganic chemical vapour deposition (MOCVD) or during post-growth processing steps needed to fabricate electronic and optoelectronic devices. On the other hand, it has been observed in experiments with intentionally introduced hydrogen that it is electrically active and behaves like an amphoteric impurity, always counteracting the prevailing conductivity. Over the years a number of tentative models has been proposed to explain this behaviour of hydrogen in silicon, binary and ternary compounds, but only recent first-principles calculations of the defect physics in these semiconductors have led to a better understanding of the mechanisms underlying the electrical activity of hydrogen.

This talk gives an overview of the present state of knowledge of the behaviour of hydrogen as a source of doping in semiconductors and of the interaction mechanisms giving rise to the passivation of the electrical activity of impurities and native defects. As examples, the results obtained for the wide-band-gap semiconductors GaN and ZnO as well as the ternary chalcopyrite compound CuInSe2 will be considered in detail. Consequences for related future experiments and for possible modifications of processing steps in device production will also be discussed.  

Speaker suggested by Mike Yakushev

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UNMISSABLE: NOBEL LAUREATE IN PHYSICS 1997

PLEASE NOTE DIFFERENT LOCATION

23 April 2003, Colville Building Room 4.20

A Bose Condensate in an Optical Lattice:
cold atomic gases meet solid state physics

Prof. William Phillips, Nobel Laureate 1997, National Institute of Standards and Technology (USA)

An atomic-gas Bose-Einstein Condensate, placed in the periodic light-shift potential of an optical standing way, exhibits many features that are similar to the familiar problem of electrons moving in the periodic potential of a solid-state crystal lattice. Differences include the distance scale of the lattice (100s of nanometers compared to a few Ångstroms) and the fact that the BEC represents a wavefunction whose coherence extends over the entire lattice, with what is essentially a single quasi momentum. Recent experiments at NIST-Gaithersburg explore the behavior of a BEC in an optical lattice and interpret the sometimes surprising results using traditional band theory.  

Speaker suggested by Erling Riis

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7 May 2003

Molecular Electron Dynamics Driven by a Strong Laser Field

Dr. Jon Marangos, Imperial College, London

The talk will begin by briefly reviewing the other work in the area of "Matter in strong laser fields and high intensity laser science" in the Blackett Laboratory. We will then discuss HHG (high harmonic generation) in molecules and laser ellipticity dependence. Recent experiments on HHG in aligned molecules will be presented and a tentative explanation for the observed alignment dependence will be put forward. We will then turn our attention to the theoretical treatment of HHG in aligned molecules and to a newly found electron wavepacket interference effect. This will lead into a discussion of the potential for electron diffraction measurements with sub-femtosecond resolution.  

Speaker suggested by Gordon Robb

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For a list of colloquia of last academic year (2001/2002) click here