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ORC Seminar Series
Controlling light at the nanoscale with plasmonic nanostructures
Speaker: Olivier J. F. Martin, Nanophotonics and Metrology Laboratory, Swiss Federal Institute of Technology (EPFL)
Date: 10 September 2009
Venue: B2/2077 LT/J
A broad variety of plasmonic nanostructures have been introduced over the last ten years. These structures can produce strong optical near-fields and exhibit specific spectral responses when they are excited at their plasmon resonance frequency. When two or more plasmonic nanostructures interact, new plasmonic modes can be created from the coupling of the modes associated with each individual structure. The optical properties of theses new modes strongly depend on the interaction between the individual structures that form the composite. Hence the optical properties of the composite system can be tuned by changing its configuration. d from a gold thin film. Two types of plasmonic modes are supported by this system: a localized plasmon in the particle and a propagating plasmon on the thin film. The interplay between these two plasmonic modes allows for tuning the response of the system. This can be achieved by changing the spacing distance d, or by modifying the permittivity εd of the spacer layer. In this case, a very broad range of resonance wavelengths can be achieved. Using such structures as building blocks, we show that it is possible to create a system where a light pulse appears to propagate backward.
In this presentation, we discuss two types of composite plasmonic nanostructures and illustrate how their optical properties can be tuned by modifying their configuration. As first example, let us consider a plasmonic antenna. This structure is made of two gold nanoparticles separated by a 30nm gap, Fig. 1. The typical length of the structure is a few hundreds of nanometers. At the plasmon resonance wavelength, a very strong field is created in the antenna gap. By changing the antenna length or the antenna gap, it is possible to continuously tune the wavelength at which this resonance occurs.
We show that plasmonic antennas can be used to selectively enhance the Raman signal from molecules in interaction with them. By tuning the length of the antenna to a specific Raman line, this signal can be selectively amplified, while the rest of the spectrum remains depleted. The same plasmonic antenna can also be used to enhance fluorescence.
Another interesting tunable plasmonic system is shown in Fig. 2; it consists of a gold particle placed at a short distance
Olivier J.F. Martin received the M.Sc. and Ph.D. degrees in physics in 1989 and 1994, respectively, from the Swiss Federal Institute of Technology, Lausanne (EPFL), Switzerland. In 1989, he joined IBM Zurich Research Laboratory, where he investigated thermal and optical properties of semiconductor laser diodes. Between 1994 and 1997 he was a research staff member at the Swiss Federal Institute of Technology, Zurich (ETHZ). In 1997 he received a Lecturer fellowship from the Swiss National Science Foundation (SNSF). During the period 1996-1999, he spent a year and a half in the U.S.A., as invited scientist at the University of California in San Diego (UCSD). In 2001 he received a Professorship grant from the SNSF and became Professor of Nano-Optics at the ETHZ. In 2003, he was appointed Professor of Nanophotonics and Optical Signal Processing at the Swiss Federal Institute of Technology, Lausanne (EPFL), where he is currently head of the Nanophotonics and Metrology Laboratory.
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