Finger on the pulse

Three UK universities are collaborating on a four-year project to develop next-generation lasers which are more flexible, easier to use, and have a far wider range of applications than existing ones.

The research aims to develop a new version of existing ultra-fast lasers that are now used in applications ranging from eye surgery to high-speed communications. These deliver extremely short bursts of light that last no longer than 100 femtoseconds, or a few billionths of a millionth of a second.

The team consists of Dr Tom Brown from St Andrews University's physics and astronomy department and colleagues at Strathclyde and Cambridge universities. They plan to build full electronic control into the lasers themselves.

One example of this would be to allow full control over the manipulation of the laser's pulse, explained Brown. 'If we can have full control to allow us to switch between generating and not-generating a pulse, that would be a real step forward,' he said.

The research also hopes to develop a laser system that would allow control over the different wavelengths at which the laser operates.



Component integration

This is a new idea for this type of short-wave laser, said Brown. He explained that to develop these new systems the team plans to integrate many of the different components now used in lasers based on semi-conductors, with modules from existing solid state- based lasers.

'We are trying to take the best bits of the different systems and build these lasers that use different technology to do the work you want to do,' he said.

There are many reasons for needing more control over lasers. For example, the ability to switch between pulsed and non-pulsed lasers would be an extremely useful tool in advanced gene therapy.

In biological applications non pulse- generating mode lasers are used to pick up and move individual cells. However to perform operations on the cells, such as piercing a hole in its surface to introduce drugs or different DNA material, a pulsed laser is needed.

The current method for switching between pulsed and non-pulsed laser operation is far from ideal.

'At the moment someone has to stand over the laser and tap a mirror,' explained Brown. 'There are ways of doing it with mechanically manipulated mirrors but to do that you have to know about how a laser works.

'We want the new laser system to be just like a black box which the user can plug in as a component without having to know what's going on in the guts of the laser itself.'

While much of the team's work is focused on gene therapy of this sort, according to Brown there are a number of other possible applications for the new lasers, such as remote-controllable lasers in the telecommunications industry.

'In telecommunications we could use them in electronic systems such as optical analogue-to-digital conversion systems as well as generating sequences of pulses, allowing us to code the lasers. This is extremely difficult to do with existing lasers,' he said.

Short-pulse lasers are also used in optical surgery. Brown said that controllable flexible lasers would be a good replacement for the existing bulky, expensive ones used by eye surgeons.

While the £3.5m EPSRC-funded project is still in its early stages, Brown said the research team has a number of ideas of how to provide ultra-fast lasers with electronic control — including introducing electrical currents into the laser cavity.



Technological advances

St Andrews has a rich history of groundbreaking laser development. A team at the university's Laser Group developed first usable versions of these short wavelength lasers about 20 years ago. However, technology soon moves on, as Brown conceded.

'We are going to try to drag the technology into the 21st century rather than leaving it behind in the 20th century.'

The project has had a number of industrial supporters, as yet unnamed, and the researchers hope to have a working prototype of the technology ready towards the end of the project.