Pulsed laser deposition: growing crystals with lasers

Sloyan, K.A., May-Smith, T.C., Sposito, A. and Eason, R.W. (2011) Pulsed laser deposition: growing crystals with lasers. Multi-disciplinary Post Graduate Showcase, Southampton, United Kingdom. 30 Mar 2011.

Abstract

When you think of a powerful laser, it's likely that you think of something big, perhaps a James Bond-style laser made of a rod of ruby crystal.
However, bigger is not always better. Lasers and other optical devices based on films a fraction of a millimeter thick can often have better performance and higher efficiency than their bulk material counterparts. They are of interest both as compact but high performance stand-alone devices and as components in photonic integrated circuits, the optical equivalent of the microchip. As such, there are a huge range of applications, from consumer electronics to healthcare lasers to chemical sensors.
Thin-film growth of many optical crystals can be prohibitively slow or costly, particularly for rapid prototyping. Pulsed Laser Deposition (PLD), however, is a relatively quick, simple and safe method of growing layers of high-quality crystalline materials, even those with more complicated structures and compositions.
An ultraviolet (UV) laser pulse is fired at a bulk target of the material to be grown. The energy of the pulse is absorbed within a small region on the target surface which heats up, first evaporating then forming a plasma plume (a process know as ablation). This plume, which contains atoms, ions and small clusters of the original material, expands forwards away from the target surface until it hits a second piece of crystal: the substrate. By heating the substrate and repeating this process many times we build up a layer of crystal with an area of around a square centimetre and a thickness anywhere from less than a nanometer to tens of microns. By controlling the energy of the pulses, size of the irradiated area, substrate temperature and a range of other parameters, we have control over the structure and composition of the resulting film.
While most PLD setups have a single laser beam and single target, our group at Southampton uses up to four UV lasers to ablate up to three targets at once or in sequence. This extension gives us a huge range of possible avenues to explore, in terms of both fundamental techniques and designer structures. We can mix plumes of different materials to obtain specific properties in the resultant film (refractive index, for example). We can compensate for any slight changes in composition during deposition. We can create sophisticated multilayer configurations, and are even working on growing graded layers, with one material merging smoothly into another. In addition to growing layers, of interest for slab lasers, disc lasers and integrated mirrors for example, further processing of a film can be carried out to obtain more complicated structures such as channel waveguides.
As a result, we have the potential to grow a host of materials and structures that are difficult or slow to grow using other deposition techniques. My research, funded by EPSRC, is concentrated on realizing this potential. I will present an overview of PLD and outline the improvements obtained using the multi-beam approach, along with some of the techniques and devices currently being developed in our group.

This record has no associated files available for download.

Contributors

Author: R.W. Eason

Download statistics