EPSAM

I obtained my BSc (Hons) in Physics with Chemistry in 2009 from Keele University. I chose to study a degree that contained both physics and chemistry modules because I've always been interested in where the two disciplines meet and crossover.  For my third year project I looked at the crystallisation rate of polyethylene terephthalate (PET) in both branched and linear form as a function of temperature through x-ray diffraction techniques. This gave me my first experience of materials research which has led me into a PhD in materials modelling under the supervision of Dr Rob Jackson.

Computer modelling of optical materials

Supervisors: Dr Rob Jackson (Keele University), Dr Mark Read (AWE).  This project is funded and supported by AWE plc.

My PhD uses the field of computational chemistry modelling to gain an insight into solid-state laser systems. These systems consist of a stable host matrix that is transparent at the wavelength required and readily forms defects that produce the electronic structure required for the laser to work. It is usually the addition of rare-earth Lanthanide ions to the host matrix that produces active laser materials. This doping process, as well as optical degrading defects, can be modelled using a variety of techniques.

The main type of modelling used in my research is atomistic force-fields, which describes the unit cell of the system at the atomic level with the interactions between the ions empirically fitted to a potential in a suitable form. Extensions to this are used for particular ions where properties such as polarisability needs to be taken into account.

Once an accurate model has been made, defect and solution energies can be calculated and used to determine the likely defect structure of the system. This is a vital tool in any laser application as it is the defects within the host matrix that produce (and affect) the optical properties.

Another field of research is modelling the surfaces of these materials. Miller Indices can be cut and various energies calculated, which can be used to predict the morphology of the crystal. Defects can again be incorporated into these models. This allows a detailed profile to be produced showing where within the system rare-earth dopants are most likely to reside i.e. at what depth from various surfaces. If defects are likely to be found in the surface layer then the energy of such a surface will be changed and, therefore, can lead to different crystal morphology. The energetic minimum location of defects will change with concentration. By modelling the surface energy changes as a function of defect concentration the morphology of the crystal can be controlled by the dopant concentration. This has important applied use.

Finally, my project is looking at not just solid-state materials for producing lasers but also 'laser cooling'. This is the process where a crystal can be reduced in temperature just by shining a laser on to it.