Tailoring the optical properties at the micro- and nanoscale is key to enable new experiments in the field of quantum optics and biophotonics. To this end, I use my strong background in numerical simulations as well as nano- and microfabrication techniques together with the expertise in spectroscopy, linear and nonlinear optics to enable and conduct experiments.
The guiding properties of polymer waveguides on a thin gold film are investigated in the optical regime. The details of propagation in the waveguides are studied simultaneously in the object and Fourier planes, providing direct measurement of both the real and imaginary parts of the effective index of the guided mode. A fair agreement between theoretical analysis provided by the differential method and experimental leakage radiation microscopy data is shown. All these tools bring valuable information for designing and understanding such devices.
Direct excitation of surface plasmon polaritons in nanopatterned metal surfaces and thin films
We present a theoretical investigation of the local launching of surface plasmon polaritons (SPPs) by means of metal nanostructures. Efficient conversion of a propagating plane wave into interface-bound SPPs is achieved through grooves in the surface of bulk metals or slits in thin metal films. The incident light excites not only SPPs at the metal surface but also the electromagnetic modes inside the groove, which behaves like a cavity so that its width and depth have a strong impact on the SPP excitation efficiency. The light-SPP coupling can furthermore be improved by several grooves interfering constructively. Tuning the width of a slit in a thin metal film allows us to preferentially excite either one of the two fundamental SPP waveguide modes of the system, namely either the mode propagating at the upper metal interface or its counterpart at the lower interface. Maximum conversion efficiencies of more than 50% can be achieved with optimized geometries.
Direct excitation of surface plasmon polaritons in nanopatterned metal surfaces and thin films
We present a theoretical investigation of the local launching of surface plasmon polaritons (SPPs) by means of metal nanostructures. Efficient conversion of a propagating plane wave into interface-bound SPPs is achieved through grooves in the surface of bulk metals or slits in thin metal films. The incident light excites not only SPPs at the metal surface but also the electromagnetic modes inside the groove, which behaves like a cavity so that its width and depth have a strong impact on the SPP excitation efficiency. The light-SPP coupling can furthermore be improved by several grooves interfering constructively. Tuning the width of a slit in a thin metal film allows us to preferentially excite either one of the two fundamental SPP waveguide modes of the system, namely either the mode propagating at the upper metal interface or its counterpart at the lower interface. Maximum conversion efficiencies of more than 50% can be achieved with optimized geometries.
Two Particle Enhanced Nano Raman Microscopy and Spectroscopy
Phillip Olk,
Jan Renger,
Thomas Härtling,
Marc Tobias Wenzel,
Lukas M. Eng
The distance- and polarization-dependent near-field enhancement of two coupling metal nanoparticles (MNPs) is analyzed by means of the novel scanning particle enhanced Raman spectroscopy (SPRM) technique. In contrast to single MNP Raman experiments, the near-field coupling between two dissimilar MNPs as followed here leads to a Raman hot spot yielding an extra enhancement factor of 17.6 and 20, as proven here both in experiment and in theory. Three-dimensional electric field calculations for our two-particle arrangements were performed using the semianalytical multiple-multipole method. An excellent agreement is found to our experiments, in which we inspect the interaction between a “scanning” 30 nm gold MNP (Au30) and a “fixed” 80 nm Au MNP (Au80). The Au80 MNP is attached to the apex of an optical fiber manipulator and exposed to the Gaussian focus of a high NA = 1.45 objective at λ = 532 nm. A monolayer of 1-octanethiol molecules covering the Au80 MNP serves as the electric field prober when scanning the Au30 MNP through the optical focus. This constellation allows recording the Raman signatures from a very low number of well-confined molecules. Moreover, also the spectral and spatial dependence could be explored with a superb sensitivity and very low integration time.
