Atomic clocks are the most accurate and precise time and frequency standards known up to now. Professor Dong-Eon Kim’s research team at MPC-AS has successfully verified that Surface Plasmon (SP) maintains the properties of light at the atomic clock level of precision.

SP is a collective electron oscillation at a metal-dielectric interface excited by a light. The resonant interaction between electrons and the electromagnetic field of the light at the surface leads to the formation of SPs. Interest in SPs has been renewed because of the recent advances in nanotechnology that allow one to fabricate and characterize metals on the nanometer scale.

According to classical optical theory, if the diameters of holes are smaller than the wavelength of a light, light cannot pass through holes. However, thanks to SP, the light energy is converted into the SPs on the metallic surface. These SPs will be in resonance with the pitch of the holes and funnel through the nano-holes. The transmitted SP will then re-radiate in the form of an electromagnetic wave.

The method in which one can control and utilize SPs to concentrate and channel light in a sub-wavelength scale has opened a new branch of photonics using SPs, called plasmonics. Furthermore, SPs are currently being explored for their potential in many fields such as bio/chemical spectroscopy, optical communication, and nanoscale photonics. However, there has not yet been a study on the difference/distortion between electron oscillation frequency and excited electromagnetic (light) frequency.

Professor Kim’s research team set out to clarify the existing assumption that the collective electron oscillation can precisely follow the frequency of excited light frequency. Team utilized an optical frequency comb consisting of millions of optical modes with equally spaced frequencies referenced by an atomic clock. By observing that the frequency stability of the transmitted light is almost the same as the stabilized optical frequency comb, the team verified that the SP can oscillate in the same way as the light wave.

The findings, published in Nature Communications, indicate that optical frequency combs in plasmonics can be used in various advantageous ways such as ultra-precision spectroscopy, quantum information carrier, or optical ruler. Furthermore, all these intriguing applications can be integrated in a plasmonic device and enable downsizing of respective systems to a nanometer scale.