Propagation of nanoconfined light

With our unique phase-sensitive time-resolved near-field microscope we have measured the photonic bandstructures of guided modes in photonic crystal waveguides. Bloch harmonics, which together make up a Bloch mode, were observed in up to 4 Brillouin zones. By combining time sensitivity and access to the wavectors of excited photonic eigenmodes, we tracked photonic eigenstates in reciprocal space on a femtosecond timescale. With this “k-space tracking” the dynamics and coupling of eigenstates that overlapped in real space was determined.
We have shown the adiabatic transformation of one specific surface plasmon waveguide mode to a Sommerfeld-like plasmon mode that subsequently allowed nanofocusing, which was used to enhance the yield of nonlinear processes. This mode tranformation also provided efficient coupling of light from the macroscopic world to highly confined plasmonic nanowires (as small as 40 nm), which were found to exhibit significant transmission efficiencies around bend radii as small as 1 μm.