High pressure studies of Quantum
Cascade Lasers
Supervisor: Dr Ben Murdin
Major Aims:
To assist the development
of room temperature operating semiconductor lasers in the 3-20micron wavelength
region of the infrared
Techniques used and source
of expertise:
Mid-infrared spectroscopy
of semiconductor lasers will be used in conjunction with a high pressure
compressor. There are opportunitites for ultrafast laser spectroscopy of
these devices as well.
Mid-infrared spectroscopy
is very useful in the fields of semiconductor physics and elsewhere, in
particular due to the different vibrational frequencies which different
chemical bonds produce. It enables detection of molecular species and this
is important for a broad range of applications. This is normally only possible
in a laboratory environment, with a large spectrometer. With the possibility
of small, cheap, efficient lasers operating in this region it becomes possible
to have monitors of pollution, chemical process, medical diagnosis, all
for use "in the field". Eg diabetics would like to have a non-needle based
glucose monitor, and as glucose absorbes preferentially light at 10 microns
wavelength it may be possible with one of these lasers.
Unfortunately such lasers
are very inefficient and usually require cooling. A new concept in semiconductor
lasers is the so called Quantum Cascade, whereby electrons tumble from
state to state within the conduction band of the device emitting photons
as they go. In more conventional devices they all jump at once from conduction
to valence bands to give out the photons. There are several advantages
and disadvantages of this new scheme, and the project is to study the possibility
to eliminate the disadvantages. This will be done by squeezing them in
our new 10000 atmosphere gas compressor. Compressing semiconductors moves
the states around in a controlled way and allows you to understand which
are important and which less so.
The project is in collaboration
with Thales-CSF (formerly known as Thomson-CSF) in Paris where the lasers
are made.
