PhD Defense: Theory of plasmon-enhanced spectroscopy of molecular excitations: infrared absorption, fluorescence, and Raman scattering
CFM Seminars
- Speaker
-
Tomas Neuman (Theory of Nanophotonics group)
- When
-
2018/11/14
12:00 - Place
- CFM Auditorium
- Add to calendar
- iCal
**Supervisor:** Javier Aizpurua
**Research group:** Theory of Nanophotonics
[ **Download pdf**](http://cfm.ehu.es/view/files/ThesisTomasNeuman.pdf)
### **Summary**
The color of light, i.e., its spectral properties, not only pleases our eye
but also helps us to analyze the chemical nature of matter when used as a
probe in optical spectroscopy. By shining light on an unknown chemical
substance (sample), and collecting the emitted or transmitted light, it is
possible to identify characteristic spectral fingerprints that reveal the
sample’s chemical structure. For example, molecular vibrations can result in
absorption of electromagnetic radiation at the infrared end of the
electromagnetic spectrum or give rise to Raman peaks when illuminated by a
coherent monochromatic visible laser. Upon illumination, matter can also emit
fluorescence photons which find their application in modern microscopy,
spectroscopy, and in more exotic fields such as quantum computing.
Unfortunately, many of these applications are often hindered due to the
generally weak interaction between small quantities of molecules and light.
![](http://cfm.ehu.es/view/files/Tomas_newman_fig-1024x285.png)
_Figure. Schematics of mechanisms leading to plasmon-enhanced spectroscopy.
Interaction of light with excitations in molecules can be enhanced if
molecules are placed close to surfaces of metallic nanoparticles supporting
localized surface plasmons. This plasmon-mediated light-matter interaction can
give rise to signal enhancement in the so-called surface-enhanced spectroscopy
as shown in the figure, from left to right, for surface-enhanced infrared
absorption spectroscopy (SEIRS), surface-enhanced Raman scattering (SERS), and
surface-enhanced fluorescence (SEF), respectively._
Surface plasmons, the oscillation of surface charge density at the surface of
a metallic surface due to the collective excitation of free electrons, give
rise to a suitable platform to enhance the coupling between molecular
excitations and light. Plasmons are able to localize electromagnetic near
fields close to the particle’s surface and simultaneously strongly interact
with incident light. These plasmonic excitations thus facilitate the efficient
interaction between incident light and samples placed in the vicinity of the
metallic particle, an effect which can be exploited to improve the performance
of optical and infrared spectroscopies, such as in surface-enhanced Raman
scattering (SERS), in surface-enhanced infrared spectroscopy (SEIRS) or in
surface-enhanced fluorescence (SEF).
This thesis combines classical and quantum approaches to theoretically
describe the interaction among excitations in molecules, plasmons, and
electromagnetic radiation, ranging from vibrational excitations interacting
resonantly with infrared electromagnetic radiation to optically active
electronic excitations in organic dyes. Some results of the thesis, such as
the optimization of linear plasmonic antennas for SEIRS, are of practical
importance, others, including the quantum description of plasmon-exciton
coupling or the optomechanical description of resonant SERS, address more
fundamental aspects of light-matter interaction.