LED-powered laser on a low-cost wavelength

Scientists at St Andrews University have developed a low-cost laser with tuneable wavelengths that can be powered by a simple light-emitting diode (LED).

The technology consists of a corrugated polymer film on a transparent silica substrate, which converts light from a commonly available nitride LED into a laser. The polymer can be designed to tune the laser to a range of wavelengths and produce lasers in a variety of colours.

The new laser source could be used in applications such as point-of-care diagnostic devices, chemical sensing and decorative light displays.

‘The idea is that polymer lasers would be convenient, visible light sources that could be easy to make. but until now they have needed another laser, generally much more expensive and much bigger, to make them work,’ said Prof Ifor Samuel, one of the project leaders.

‘What we have done is show that it is possible to make the laser work by exciting it with a nitride LED — and LEDs are very widespread.’

The different wavelengths and colours can be produced in two main ways. One way to change the laser colour would be to adjust the size of period corrugation, which is roughly 400nm, in the polymer film.

‘In a laser you need to have a resonator, which is usually a pair of mirrors, but in our case, we made a corrugated polymer film and the corrugation acts like a diffraction grating so it changes the direction of the light travelling in the film,’ said Samuel.

Another technique would to be to use different polymer materials.

‘Compared with materials such as silicon, polymers give quite broad emission spectrums. So you could span from yellow to orange to red with just one LED pump and one polymer laser material. If you wanted to go further green and turquoise, you would need a different material,’ said Samuel.