John
Anderson
Research
Colloquia in Physics
October 2001 - August 2002
17
October 2001
Quantum Catastrophes
Prof. Ulf Leonhardt, University of St. Andrews, Scotland
Catastrophes are at the heart of many fascinating optical
phenomena. The rainbow, for example, is a ray catastrophe where
light rays become infinitely intense. The wave nature of light
resolves the infinities of ray catastrophes while drawing delicate
interference patterns such as the supernumerary arcs of the
rainbow. Black holes cause wave catastrophes. Waves oscillate
with infinitely small wave lengths at the event horizon where
time stands still. The quantum nature of light avoids this higher
level of catastrophic behaviour while producing a quantum
phenomenon known as Hawking radiation. As the lecture explains,
light brought to a standstill in laboratory experiments can
suffer a similar wave catastrophe caused by a parabolic profile
of the group velocity. In turn, the quantum vacuum is forced to
create photon pairs with a characteristic spectrum. The idea may
initiate a theory of quantum catastrophes, in addition to
classical catastrophe theory, and the proposed experiment may
lead to the first direct observation of a phenomenon related to
Hawking radiation.
31
October 2001
Confocal Microspectroscopy
using Laser and Synchrotron
Radiation
Dr. Mark Tobin, Daresbury Laboratory, England
Most commercial confocal microscope systems operate with fixed wavelength
lasers as the source of illumination. A synchrotron radiation source,
however, provides easily tuneable, continuous UV-visible radiation which can
be used as the excitation source. With the storage ring operating in single
bunch mode, the pulsed time structure is also ideally suited for
fluorescence lifetime spectroscopy, even though a typical wavelength
filtered beam may be several orders of magnitude less bright than a
comparable laser. The Daresbury Laboratory confocal microscope, SYCLOPS
(SYnchrotron Radiation for ConfocaL OPtical Scanning) combines these useful
properties of SR with a highly adaptable optical configuration to provide a
versatile spectroscopy and imaging facility. Further developments have
included the addition of a multielement spectrograph for microspectroscopy
measurements, which was funded through a grant obtained by Strathclyde
University.
SYCLOPS is used by several research groups from UK universities, and each
group makes use of the on-line and off-line advantages of the instrument.
For example:
1) Time resolved fluorescence and UV imaging have been used to study a range
of nitride semiconductors. The distribution of fluorescence from samples,
and the fluorescence lifetime of microscopic features can provide
information on the material composition.
2) UV imaging and time resolved fluorescence has been used to study the
interaction of plant-derived oestrogen-like molecules (phyto-oestrogens)
within human cells. These molecules are of importance since they have been
implicated in low sperm count in humans and feminisation of fish. The
fluorescence lifetime of one particular phyto-oestrogen is sensitive to its
environment and time resolved UV fluorescence microspectroscopy has been
used to look at the binding state in living cells.
3) Photosynthesis of several plant species is being studied as a potential
monitor of environmental pollution and fungal infection. Again the
fluorescence lifetime of small areas of leaf, and even single chloroplasts,
provides important information on the condition of the plant.
14
November 2001
Amorphous silicon
devices: from the very large to the very small
Dr. Mervyn Rose, Display Technology, University of Dundee, Scotland
Amorphous silicon is a thin film semiconductor that forms the basis of large
area electronics. There is already a world-wide industry in solar cells and
electronic displays based on amorphous silicon devices. This talk will
review some of these technologies and give some examples of our latest
research that aims to make more cost effective solar cells and more easily
manufactured displays. A new thin film field emission display device will be
described based on thin film laser processing.
But amorphous silicon is also being used for ultra-small devices and we will
look at a new non-volatile memory technology. These devices form microscopic
permanent filaments that switch between states on very fast time scales with
low voltages and are very robust. Under certain conditions we can see what
appear to be single electron effects and quantized resistance.
28
November 2001
Growth of Gallium Nitride
and related semiconductors by metal organic chemical vapour deposition
Dr. Ian Watson, Institute of Photonics, University of Strathclyde
Gallium nitride (GaN) and related wide-bandgap semiconductors have achieved
growing practical importance over the past decade. The best known devices
based on these materials are blue and green light-emitting diodes, although
laser diodes, photodetectors and field effect transistors are also now
commercially available. Advances in large-scale production of epitaxial
nitride device structures have depended to a considerable extent on applying
the metal organic chemical vapour deposition (MOCVD) technique, which
matured as a method for producing other compound semiconductors during the
1980s, to the more challenging nitride systems. The University of
Strathclyde achieved its own nitride MOCVD capability in mid-2000, with the
commissioning of a reactor operated by Institute of Photonics researchers at
the off-campus Compound Semiconductor Technologies facility. Nitride MOCVD
activities are part of a wider programme involving device development and
innovative processing, but this talk will concentrate particularly on
characterisation of the growth process itself, and post-growth
investigations of materials properties. A combination of analysis techniques
is frequently needed to give a useful understanding of samples. Some of the
most valuable methods include in situ measurements of optical reflectance
during growth, and post-growth luminescence-based characterisation performed
by colleagues in the Department of Physics and Applied Physics. One topic of
special interest is growth of ternary indium gallium nitride (InGaN) layers,
which, when fabricated in the form of quantum wells (QWs) only a few
nanometres in thickness, constitute the active region of visible
light-emitting devices. Examples will be given of in situ and ex situ
characterisation of InGaN-based structures containing both thin QW layers,
and thicker epitaxial layers offering more scope for direct compositional
and structural analysis.
Please note that the Colloquium of Dr. Pierre Lefebvre, Universite' Montpellier II,
France has been cancelled.
12
December 2001
New methods for non-invasive human skin
characterisation
Prof. R E Imhof, School of Engineering, South Bank University, London, England
This talk aims to present an overview of our recent research in the
development of new methods for characterising human skin. First,
I will briefly introduce some of the background to the research,
describing the layered structure of human skin and the properties that
are accessible to measurement by our main approach of photothermal
radiometry. Then I will describe recent advances that have come from
the development of high resolution spectroscopic capabilities that can
be used non-invasively on in-vivo and in-vitro stratum corneum. The
first of these is photothermal excitation spectroscopy using a tuneable
OPO laser, with which we have studied water binding within the stratum
corneum. The second, which is still under development, is photothermal
FT-IR spectroscopy, with which we can perform non-invasive spectral depth
profiling measurements on arbitrary surfaces. The final part of the talk
will introduce a patented new method for measuring water loss from skin,
which is a radical departure for us, because it uses neither "photo"
nor "thermal" technologies.
9
January 2002
An unconventional quantum
system at the edge;
Physics and applications of interfaces involving high-Tc superconductors
Prof. Hans Hilgenkamp, University of Twente, The Netherlands
A central issue in resolving the mechanism of superconductivity at high
temperatures in the high-Tc cuprates is the identification of the symmetry
of the order parameter, describing the superconducting condensate. Recently,
it has been established by various elegant experiments that this symmetry is
predominantly d-wave, with a possible admixture of smaller
symmetry-components.
This unconventional symmetry also bears important implications and prospects
for applications of high-temperature superconductors, many of which rely on
interfaces in these materials. For example, it facilitates the realization
of novel superconducting quantum-devices that include, so-called,
pi-Josephson junctions. In these devices, the pi-junctions can be considered
to exhibit a negative critical current, giving rise to various peculiar
effects.
23
January 2002
Time reversal
violation in YbF
Dr. Benjamin Sauer, Physics Department, University of Sussex, England
A non-zero value of the electron electric dipole moment d_e implies time
reversal violation which would not be compatible with the Standard Model of
particle physics. The most sensitive measurements of d_e have been made
using heavy atoms. In principle, heavy polar molecules offer a greater
sensitivity to d_e because the interaction energy to be measured is
typically 10^3 times larger than in a heavy atom. I will report the first
measurement using a heavy molecule, YbF. Because of the large interaction
energy and the cylindrical symmetry of the YbF molecule, the experiment
does not encounter the systematic effects which limit the atomic
measurements. I will discuss the current operation of the apparatus and
possible future improvements.
6
February 2002
Snowflakes,
Butterfly Wings and Plastics: New Materials for Optoelectronics
Prof. Ifor Samuel, School of Physics, University of St. Andrews
Polymers, or plastics, are familiar materials found throughout everyday
life. Polymer molecules consist of many repeat units, and the enormous
range of possible repeat units give an almost unlimited variety of
polymeric materials. This gives great diversity, and applications
of polymers range from compact discs to bullet-proof vests and from
cling film to car tyres. Biological polymers such as DNA, proteins, and
cellulose form the basis of life itself. One of the key reasons for the
widespread use of man-made polymers is the ease with which they can be
processed into almost any desired shape or form. They can be moulded
into a particular shape, extruded to make tubes or films, or spun to
make fibres. A further advantage of polymers is that their properties
can be controlled by modifying their chemical structure. Plastics are
well known as electrical insulators, and to date have been widely used
as structural materials (e.g. for furniture, computer housings etc.),
for packaging, and as fabrics and films.
This colloquium will focus on some remarkable polymers which can conduct
electricity and emit light, opening new directions in optoelectronics
and polymer science. Semiconducting polymers are of particular interest
and can be used to make a wide range of electronic devices such as
transistors, light-emitting diodes and solar cells. They offer the
prospect of materials that combine novel electronic properties with
the ease of processing of polymers, and whose properties can be tuned
by chemical modification to give desired features. This new class of
optoelectronic materials means that we can now dream of giant flexible
displays and electronic circuits made by printing. We shall look at
the remarkable developments that have taken place in this field, giving
plastic semiconductors, transistors and light-emitting diodes, and then
consider the ingredients that will fuse to give future innovations.
PLEASE NOTE DIFFERENT TIME AND DIFFERENT LOCATION
13 February 2002, 2:00-3:00 pm in Room 8.11 John Anderson Building
Max Planck:
a life in science
Dr. Igor Jex, Technical University of Prague, Czech Republic
The life of Max Planck is reviewed. Emphasis is put on his life
as a scientist and as the organizer of scientific life in Germany.
A few comments will be made of his philosophical view. The talk is
based on my recent biography of Planck.
20
February 2002
CANCELLED (SPEAKER IS UNWELL)
Atoms in non-dissipative optical
lattices
Dr. David Meacher, Department of Physics and Astronomy, University College London
6
March 2002
The physics of plasmas across 10 orders of magnitude
Dr. Declan Diver, Department of Physics and Astronomy, Glasgow University
The non-linear behaviour of bounded, drived electric fields in
processing plasmas is central to understanding how practical plasma
reactors function, from ion acceleration to neutral transport. However,
isolated time dependent electric fields also play a basic role in
astrophysics, particularly in the context of pulsars. This talk will
present an exploration of the common plasma physics in these disparate
contexts, ranging from ion and neutral acceleration in driven sheath
fields, to pair plasma oscillations in pulsar magnetospheres and the
coupling to electromagnetic plasma waves.
20
March 2002
NO COLLOQUIUM
The Physics Department
went to the Glasgow Science Centre and had a great time !
10
April 2002
Recent developments in the atomic physics of fusion and astrophysical plasmas
Prof. Hugh Summers, Department of Physics and Applied Physics, University of
Strathclyde, Glasgow
The talk will be a review of spectroscopic analysis of plasmas carried out in
the Atoms, Beams and Plasmas group in the Department. The review will range
widely and lightly, touching on observations by spacecraft of the sun and other
astrophysical objects and on spectroscopic experiments in the European fusion
programme. The review will also range widely in species (hydrogen to uranium),
in wavelength (visible to X-ray), in thermal environment (LTE and beams) and
in radiation environment (optically thick and thin). The talk will conclude
with some speculations on expected points of focus in the next five years.
17 April 2002
Collective excitations
in unconventional superconductors
Prof. Peter Brusov, Rostov State University, Rostov-on-Don, Russia
In ordinary low-temperature superconductors (SC) with transition
temperatures Tc from normal to superconducting states less than 24K,
the mechanism of pairing is of the s-wave type. A few different types
of pairing are instead realised in high-temperature superconductors
(HTSC) with Tc in the range of 50-150K.
There are two collective modes in the ordinary superconductors: one
is coupled to oscillation of phase and the other to oscillation of
the superconducting order parameter amplitude. A few years ago the
amplitude mode with frequency of order of the superconducting energy
gap was observed in films of ordinary superconductors. The spectrum of
collective excitations in unconventional superconductors (USC) is far
richer via non trivial pairing.
The study of the collective excitations in the USC has become very
important recently. 2D and 3D models of p- and d- wave SC have been
constructed with use of the path integration technique (PIT). We study
both bulk and thin film systems. Some new ideas concerning a realization
of the mixtures of different states in HTSC are being investigated.
Results obtained so far can possibly be used for an interpretation
of sound and microwave absorption data as well as for the identification
of the actual type of pairing in USC.
I will discuss the symmetry of order parameter in HTSC and experimental
symmetry probes (where Josephson effects play a very important role).
Josephson effects in junctions made of conventional and unconventional
superconductors will also be discussed.
24
April 2002
Atoms in non-dissipative optical
lattices
Dr. David Meacher, Department of Physics and Astronomy, University College London
In this talk, I will show how the interaction between an atomic gas and a
spatially-varying optical field can be exploited to form an optical lattice,
which is an ordered structure of atoms, a gaseous analogue of the
crystalline materials found in condensed matter, bound by light. I will
describe some of the salient properties of optical lattices, as well as
their limitations and then go on to show how atoms can be transferred to an
optical lattice induced by light detuned far from any atomic resonance, so
that that dissipation due to spontaneous emission can be effectively
eliminated, and then pumped into the ground motional state by
resolved-sideband Raman-cooling. Finally, I will outline the prospects for
quantum-state engineering in non-dissipative optical lattices.
PLEASE NOTE DIFFERENT DAY AND DIFFERENT LOCATION
Tuesday 18 June 2002, Royal College Room 6.67, at 4:00 pm
Plastic micro-optical modules for parallel
free-space optical interconnects
Prof. Hugo Thienpont, Applied Physics and
Photonics Department, Vrije Universiteit, Brussel, Belgium
31
July 2002
Introduction to the Air
Force Propulsion Directorate
Dr. Alan Garscadden, Chief Scientist, US Air Force Research Laboratory,
at Wright-Patterson Ohio
A personal overview is presented on the many roles that physics
and engineering play in programs of the Propulsion Directorate,
Air Force Research Laboratory (AFRL) and subsequently on AF systems
and operations. AFRL has 10 directorates and it is also a defense
contracting and evaluation agency. The AF sponsors and pursues research
and development for several reasons:- to have a highly qualified work
force; to enhance its technology options and to provide the Air Force
with the best operational capabilities. The organization of AF science
and technology starts with AFOSR as the single manager of AF Basic
Research, (6.1). Most of this program, 70%, involves academia. Then
there are the Exploratory Development programs (6.2) managed by the
other AFRL directorates where concepts are evaluated and components
are developed. These programs involve industries and some universities,
especially in cooperation with companies. Some of the successes transition
into Advanced Development programs (6.3), where integration occurs to
provide a system or sub-system. The R&D process and planning are quite
involved and have Darwinian competitions for resources. Some example
studies, involving primarily propulsion and power for air and for space,
successful and unsuccessful, are discussed.
-
For further information contact
Prof. Gian-Luca Oppo
-
(0141-548-3761 or 0141-548-3364)
or email to
-
gianluca@phys.strath.ac.uk
For a list of colloquia of
last academic year (2000/2001) click here
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