The United Kingdom maintains a permanent station at FELIX directed and operated by two facility scientists. As a consequence of the FOM-EPSRC agreement, users from the UK take more than 20 percent of the total available FELIX beam shifts. The primary emphasis of the UK programme is semiconductor physics, in particular suppression of non-radiative processes in semiconductor mid-infrared emitters and detectors. The co-ordinator of the programme is Professor Carl R. Pidgeon of the Department of Physics , Heriot-Watt University , Edinburgh.
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Prof. Carl R. Pidgeon
Co-ordinator |
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Dr P. Jonathan Phillips Senior Facility Scientist
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Dr Damian Carder Facility Scientist |
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The programme, whats available and the people who make it happen!
The Essence of it
Narrow gap semiconductors have many unique properties which are advantageous for optical and electronic applications, and in particular for detectors and emitters of mid-infrared radiation associated with interband optical transitions. More recently systems based on inter-subband transitions have shown great promise for mid-infrared devices, with the obvious advantage for some applications that they can be constructed from large gap, better controlled materials (mainly InP- and GaAs-based to date) and have a peak operating frequency which is determined simply by the design of the particular quantum structure. Whilst quantum well intersubband photodetectors (QWIP's) are by now a relatively mature subject, it was only with the advent of cascade structures that subband lasing was first achieved. Both approaches have been substantially advanced by band structure engineering techniques, reducing Auger losses and phonon losses respectively, the essential subject of the investigations performed by the UK user consortium at FELIX.
Is that it?
Far from it. We have recently developed programmes concentrating on non-radiative relaxation of doped insulating materials. Interest in tunable solid state laser materials stems from the outstanding performances of Ti-sapphire, alexandrite (Cr3+:BeAl2 O4)and forsterite (Cr4+:MgSiO4 ). Non-radiative relaxation represents a serious limitation to the development of room temperature solid state lasers operating in the near- and mid-infrared regions. Recent work has shown that localised vibrations of the optically active center can be critical in the non-radiative energy transfer process from the electronic states of a given impurity and the lattice band modes. However we know little about the time evolution of these modes during the optical pumping cycle. A novel approach is to engineer 'model' modes which can be treated in isolation from the complicated coupled electron-lattice systems which exist in real laser gain media. An example of such vibrational systems are the H- localised vibrational modes which can be created in ionic crystals. These systems can be conveniently studied using FEL's and form a 'second string' of research performed in an international collaborative effort.
You say you want more...
As a collective group of scientists
we are interested in pushing the research into the coherent regime
which enables one to study effects within the generally inhomogeneously
broadened absorption profiles observed in (for example) semiconductor
quantum wells or dots. This also applies to vibrational systems where we
have performed quantum beat spectroscopy of the overtone spectrum of
several vibrational systems using a coherent transient technique called
"Free induction decay" . To do this, we utilise the ultra-short (actually
sub-picosecond) pulse capabilities of FELIX in conjunction with a 9
femtosecond Ti-sapphire laser and 100-200 femtosecond infrared optical
parametric oscillators available at the facility.
The UK User Station, US3.
The UK has it own permanent work
station at FELIX. The UK user station contains an assortment of equipment,
including an optical bench, optics, mounts, tools, a Stanford
research lock-in, Keithley 236 source measurement unit, Keithley DVM,
preamps, oscilloscopes, cryostats, magnets, delay stages and vacuum
equipment for long wavelength experiments. Recently we bought an ISA Triax
33, a 33cm triple grating spectrometer, with gratings for use in the
spectral regions from 400 nanometres to 18 micrometres. Most of the equipment
is controlled with programs written in Labview. Check it all out in
here
Annexed Territory - The Non-Linear
Optics Lab, US4.
Actually we do alot of work using
this station. There are two permanent systems for long (30 -250 micron)
and short wavelength (3 - 30 micron) designed to be configured for
multi-colour two/three beam pump and probe measurements, two pulse and
stimulated photon echo/free induction decay experiments as well as transient
gratings. Your imagination is the limit. See all in
here
The 45T Pulsed Magnet Facility,
US8.
Despite its name this is a conventional
pulsed magnet, with optical access, capable of fields up to 45 Tesla
with a magnetic field rise time matched to the macropulse length of
FELIX. Have a pulsating time in
here