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Surface-enhanced optical spectroscopies

The research area of field enhancement in metal nanostructures is concerned with the relation between a given light illumination and local electric fields resulting at the sample due to the illumination. A rather simple, still controllable illumination could be from a halogen light bulb in a standard optical microscope, where it is then possible to observe different colors from the nanostructures depending on their (measurable) reflection, transmission, absorption, and scattering spectra. Dependent on the exact nanoparticle geometry, material properties and combined influence of neighboring nano-particles and substrate each configuration will lead to possible localized surface plasmon resonances, which can be probed with more accurate light sources such as femto-second lasers focused to diffraction-limited spots being scanned across at the sample. The ultra-short pulses facilitates high peak intensity while the average intensity remains low enough to avoid thermal sample damage. The resonance in the nanostructures then lead to further local intensity enhancement and so-called hot-spots, with significantly increased probability of nonlinear processes, e.g., two incident photons can be absorbed by the metal nanostructure at the same time and then re-emitted as two-photon photoluminescence (TPL), estimating the local enhancement. Once promising nanoparticle configurations are located, we apply these for surface enhanced Raman spectroscopy (SERS), which give fingerprint information about various molecules adsorbed close to the resonant nanoparticles and in hot spots. We are using both linear spectroscopy, as well as TPL and SERS characterization in several projects, including self-assembled nanostructures and sensing applications. In addition, we have even used Raman microscopy to differentiate normal vs. abnormal human embryonic stems cells.

 Here are some of our research papers for further details:

  • Enhancement of two-photon photoluminescence and SERS for low-coverage gold films, Opt. Express 24, 16743-16751 (2016).
  • Light extinction and scattering from individual and arrayed high-aspect-ratio trenches in metals, Phys. Rev. B. 24, 93:075413 (2016).
  • Plasmonic black metals via radiation absorption by two-dimensional arrays of ultra-sharp convex grooves,Sci. Rep 24, 4, 6904 (2014).
  • Optical spectroscopy of single Si nanocylinders with magnetic and electric resonances, Scientific Reports 4 24, 4126 (2014).
  • Polarization-resolved two-photon luminescence microscopy of V-groove arrays, Opt. Express, 20 24, 654-662 (2012).
  • Tuning surface plasmons in interconnected hemispherical Au shells, Opt, Opt. Express, 20 24, 534-546 (2012).
  • Identification of Abnormal Stem Cells Using Raman Spectroscopy, Stem Cells and Development, 21 24, 2152-2159 (2012).