Researchers sculpted a metallic structure, dubbed a plasmonic collimator, consisting of an aperture and a periodic pattern of sub-wavelength grooves, directly on the facet of a quantum cascade laser emitting at a wavelength of ten microns, in the invisible part of the spectrum known as the mid-infrared where the atmosphere is transparent. In so doing, the team was able to dramatically reduce the divergence angle of the beam emerging from the laser from a factor of twenty-five down to just a few degrees in the vertical direction. The laser maintained a high output optical power and could be used for long range chemical sensing in the atmosphere, including homeland security and environmental monitoring, without requiring bulky collimating optics.
"It is an important first step towards beam engineering of lasers with unprecedented flexibility, tailored for specific applications. In the future, we envision being able to achieve total control of the spatial emission pattern of semiconductor lasers such as a fully collimated beam, small divergence beams in multiple directions, and beams that can be steered over a wide angle."