Nonlinear excitation of graphene plasmons

The nonlinear response of graphene enables excitation and detection of plasmons using far-field optics

Surface plasmons in graphene offer a compelling platform for photonic technologies, exhibiting intriguing properties such as electro-optical tunability, a very small wavelength, and high electromagnetic field concentration. Graphene plasmons also exhibit a large bandwidth, extending into the far infrared. Some of these properties simultaneously make graphene plasmons difficult to excite and detect, due to the large mismatch between the wavelengths of free-space and plasmon fields, and the need for sources and detectors at unconventional frequencies.

nphys3545-f1An experimental research team led by Prof. Euan Hendry at Exeter University, in collaboration with the theory group of Prof. Darrick Chang at ICFO, has demonstrated an appealing alternative to exciting and detecting graphene plasmons, which was recently published in Nature Physics. In this work, the team demonstrates that graphene exhibits a giant nonlinear optical response, which can be used to convert free-space optical beams to plasmons of a well-defined frequency and direction via a coherent mixing process. The excitation of plasmons is inferred by a change in reflection of the input fields. Interestingly, all of the optical sources and detectors used in the experiment operated at visible wavelengths, yet it was possible to generate plasmons at frequencies down to the far infrared. The potential to excite and detect plasmons only with free-space optics, and at frequencies significantly different than that of the plasmons themselves, has the potential to significantly expand the technological possibilities for graphene plasmonics.

The new research features in the latest online edition of the respected scientific journal, Nature Physics.

Dr. Tom Constant, lead author on the paper and part of Exeter’s Physics and Astronomy Department said: “ This new research has the potential to give us invaluable insight into the wonder material and how it interacts with light.

A more immediate commercial application could be a simple device that could easily scan a piece of graphene and tell you some key properties like conductivity, resistance and purity .”

Dr. Constant and his colleagues used pulses of light to be able to trap the light on the surface of commercially-available graphene. When trapped, the light converts into a quasi-particle called a ‘surface plasmon’, a mixture of both light and the graphene’s electrons.

Additionally, the team have demonstrated the first example of being able to steer the plasmons around the surface of the graphene, without the need to manufacture any complicated nanoscale devices.

The ability both to trap light at a surface, and direct it easily, opens up new opportunities for a number of electronic-based devices, as well as help to bridge the gap between the electronics and light.

Dr. Constant said: “Computers than can use light as part of their infrastructure have the potential to show significant improvement. Any advance that reveals more about light’s interaction with graphene-based electronics will surely benefit the computers or smartphones of the future.”

Link to paper
Research Group led by Professor Euan Hendry
Research Group led by Professor Darrick Chang