Leakage Radiation Microscopy C E GarciaOrtiz October 2012

Leakage Radiation Microscopy 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 �Direct, and Fourier space imaging �Filtering in LRM

Surface plasmon polaritons (SPPs) Surface plasmon resonance Kretschmann configuration

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

Leakage radiation (LR) SPP nglass q. LR 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.

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 Metal Dielectric (n) kspp q. LR k. LR = nk 0 k. LR x And since the frequency do not change

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

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

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 NA 1 is directly dependant on the neff of the SPP. The limiting case occurs when q = q. LR and this yields For our previous example we can calculate the neff

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

Local excitation of surface plasmons

The leakage radiation experimental setup Laser

LRM imaging examples C. Garcia et al, Appl Phys B Laser Optic, Vol. 107, No 2 (2012) A B

Direct and Fourier space

The Fourier plane ky k. SPP LR TL kx

Filtering in LRM: Fourier transform and filters

Without filtering Transmitted light is filtered Desired image (well filtered)