Researchers have found evidence to suggest that two lasers are not necessarily brighter than one. Moreover, the findings of a study led by scientists at the Technische Universität Wien (TU Wien), in collaboration with Princeton University, Yale University and Eidgenössische Technische Hochschule Zürich (ETH Zürich), seem to demonstrate that two laser beams shining next to one another can actually cancel one another out.
In order to shine, lasers must be supplied with energy, or 'pumped'. By gradually 'pumping' one laser situated next to another that was already shining, the team, whose results have been published in the journal Physical Review Letters
, discovered an apparently 'paradoxical' phenomenon; that two lasers do not necessarily result in twice the brightness, and that in combination, the beams can lead to a total shutdown during which no light is emitted.
"Imagine two light bulbs right next to each other, one of which is switched on," said Matthias Liertzer from TU Wien's Institute for Theoretical Physics. "As you gradually turn on the second bulb by adjusting a dimmer switch, you expect the room to get brighter." However, Liertzer and his colleague, Professor Stefan Rotter, used computer simulations to study the behaviour of coupled micro-lasers, and did not find this to be the case during their experiments.
"When we saw that the two lasers can switch each other off completely, due to the coupling between them, we knew: either we made a mistake or this is a spectacular result," explained Professor Rotter.
Light consists of waves, and waves can interfere with, and cancel one another. Whilst the team believes that this interaction forms part of the explanation, they contend that the precise reason is more complex.
"This effect is not just about wave interference," said Liertzer. "It is a combination of interference and light amplification, which can lead to seemingly paradoxical effects."
Mathematicians at TU Wien believe that exceptional points, or special intersections of surfaces in complex spaces, play an important role in this process.
"The phenomenon is based on what mathematicians call exceptional points," said Professor Rotter. "The appearance of such exceptional points in our laser equations can lead to a laser blackout. In this way we could connect a rather abstract mathematical structure to a measurable phenomenon."
The effect has been confirmed in independent calculations conducted by the study's Yale-based co-authors, and electrical engineers at the TU Wien, who are currently experimenting with micro-lasers, hope to further corroborate the findings. It is thought that these results could be applied by those looking to use laser light for the transmission of computer data.