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Leakage Radiation M icroscopy

Leakage Radiation M icroscopy. C.E . Garcia -Ortiz October , 2012. Outline. Introduction to LRM Surface plasmon polaritons Imaging techniques Leakage radiation Numerical aperture and effective index Local excitation The LRM setup LRM imaging examples

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Leakage Radiation M icroscopy

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  1. Leakage Radiation Microscopy C.E. Garcia-Ortiz October, 2012

  2. Outline • Introduction to LRM • Surface plasmon polaritons • Imaging techniques • Leakage radiation • Numerical aperture and effective index • Local excitation • The LRM setup • LRM imaging examples • Direct, and Fourier space imaging • Filtering in LRM

  3. Surface plasmon polaritons (SPPs) Kretschmannconfiguration Surface plasmon resonance

  4. Plasmonics Imaging techniques SNOM Scanning Near-field optical microscopy LRM Leakage radiation microscopy TPL Two-photon luminescence

  5. Leakage radiation (LR) SPP nglass qLR LR LR Due to boundary conditions and conservation of the in-plane wave-vector along the different interfaces, SPPs leak through the thin gold film into the glass substrate. Leakage-radiation microscopy (LRM) consists in detecting these leaky waves.

  6. Wave-vector in-plane conservation One boundary condition that must be satisfied is that the phases of the waves must match at the interface (z = 0) at all times. z kspp Metal x And since the frequency do not change Dielectric (n) kLR qLR kLR= nk0

  7. Leakage radiation cone SPP H. J Simon, J. K. Guha, Opt. Comm. 18, 391 (1976). nglass Example: Lets put somenumbers to theseequations… qLR LR LR B. Hecht, D. Pohl, H. Heinzelmann, and L. Novotny, Ultramicroscopy 61, 99 (1995).

  8. Problem with common substrates Total internal reflection SPP LR qLR nglass Leakage radiation can not get out! Solution Refractive index matching liquid SPP Refractive index matching liquid (Oil) LR qLR nglass Objective lens Oil Immersion Microscope Objective

  9. The SPP effective index neff and the numerical aperture (NA) The numerical aperture (NA) of an objective is related to the work distance and size of the lens aperture. The NA is given by If we have an objective with a NA = 1.25, it can accept light at a maximum angle q = 56°. The SPP effective index The LR that can be detected with an objective of numerical aperture NA1 is directly dependant on the neff of the SPP. The limiting case occurs when q = qLR and this yields For our previous example we can calculate the neff

  10. Local excitation of surface plasmons Incident beam SPP Refractive index matching liquid (Oil) LR qLR nglass Objective lens Oil Immersion Microscope Objective

  11. Local excitation of surface plasmons

  12. The leakage radiation experimental setup Laser

  13. LRM imaging examples A B C. Garciaet al, ApplPhys B Laser Optic, Vol.107, No 2 (2012)

  14. Direct and Fourier space

  15. The Fourier plane ky kSPP LR TL kx

  16. Filtering in LRM: Fourier transform and filters

  17. Withoutfiltering Transmitted light isfiltered Desiredimage (wellfiltered)

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