FOM researchers design new type of laser
Researchers from the FOM Foundation, Leiden University, Eindhoven University of Technology and Philips Research have made a new type of laser. This laser makes use of light beams that are trapped on a metal surface, so called surface plasmons. As these trapped light beams are far more compact than light in free space, they offer the possibility of making ultrasmall lasers which can for example be used in computer screens. What makes the new system unique is that in various ways, the researchers have demonstrated that the laser light in their system really does originate from surface plasmons. They published their work on 13 May in Physical Review Letters.
The new surface plasmon laser consists of a thin gold surface containing about 1000 miniscule holes, a design not previously used. The holes reflect the surface plasmons, converting these into normal light. The grating is stuck to a material that further amplifies the light. Once the total light amplification is sufficient, the light acquires the characteristic properties of a laser: a bright, well-focused beam of a single colour.
Light patterns
"What makes our experiments so special is that we can very clearly demonstrate that the surface plasmons are responsible for the laser effect," says FOM workgroup leader Dr. Martin van Exter. With earlier surface plasmon lasers that was not so simple to establish. To determine the role of the surface plasmons, the researchers studied the light patterns emitted. From these they deduced that the surface plasmons were reflected in the grating and how this occurred.
"We can learn three things from these patterns. First of all, each pattern has a vertical and a horizontal line of symmetry just like the grating. This indicates the patterns are determined by the square grating. Secondly, the patterns indicate that the light travels across the gold surface," says Van Exter. Each horizontal and vertical line in the light pattern agrees with a surface plasmon. "Finally, we could observe that the surface plasmons were reflected back and forth through the holes," says Van Exter. The scientists could deduce that last characteristic from the abnormal shapes in the light patterns, such as light rings. These patterns only arise if the surface plasmons are reflected in the grating.
Thickness of a single hair
Lasers are used in a wide range of applications from DVD players to medical applications. With the plasmon technique, lasers can be made even smaller still. The current surface plasmon laser is just a few thousands of the thickness of a single hair, but the researchers think it might be possible to make the system even thinner still. Also the number of holes could possibly be reduced from the current thousand to just several dozen. In the future, the plasmon technology could find uses in computers or screens.
Contact
Dr. Martin van Exter, +31 (0)71 527 59 27 or +31 (0)71 527 58 96
Reference
'Surface Plasmon Lasing Observed in Metal Hole Arrays' Frerik van Beijnum, Peter J. van Veldhoven, Erik Jan Geluk, Michiel J. A. de Dood, Gert W. ’t Hooft, and Martin P. van Exter. Physical Review Letters 13 May 2013.