H. Gersen

On the role of electromagnetic boundary conditions in single molecule fluorescence lifetime studies of dyes embedded in thin films

Single molecule fluorescence lifetime studies are generally performed in thin polymer films, where the influence of the interface on the behaviour of fluorescing molecules is not negligible. In order to describe this influence, we investigate annealed films of different thickness. We show that the distribution of fluorescence lifetimes of the embedded dyes is shifted to lower values as the thickness of the film increases. We explain this shift by simple electromagnetic arguments related to the boundary conditions at the interfaces of the polymer film with air and glass, respectively. The conclusion is that extreme care must be taken in order to interpret single molecule data with respect to the true chemical nature of the phenomena.

Near-field effects in single molecule emission

We present the first experimental proof of the influence of a nearby nano‐sized metal object on the angular photon emission by a single molecule. A novel angular sensitive detection scheme is implemented in an existing near‐field scanning optical microscope (NSOM). The positioning accuracy (∼1u2003nm) of the NSOM allows a systematic investigation of the intensity ratio between two different half‐spaces as a function of the position of the metal–glass interfaces of the probe with respect to the single emitter. The observed effects are shown to be particularly strong for molecules that are excited mainly below the rims of the aperture. An excellent agreement is found between experiments and numerical simulations for these molecules. The observed angular redistribution of the angular emission of a single molecule could explain the alteration of the emission polarization observed for certain molecules in earlier experiments (Veerman et al.(1999)J. Microsc.194, 477–482).

Local investigation of photonic crystal devices in space and time

In this paper, the investigation of light propagating inside such a structure is usually limited by both the diffraction limit and the absence of radiating light. We have solved this by investigating a photonic crystal waveguide with a phase-sensitive time-resolved near-field scanning microscope. Photonic crystals are promising structures for controlling light, because the light has to obey Blochs theorem. The resulting control over optical dispersion allows time control in integrated optical structures and enhancement of light-matter interactions

Pulse tracking in complex photonic structures

Time-resolved near-field microscopy allows the propagation of ultrafast pulses to be visualized en route while they travel through complex photonic structures. These measurements enable the unambiguous determination of both local phase and group velocities. We illustrate this powerful technique by tracking an ultrashort wavepacket as it completes several round trips in a ring resonator.

Optimization problems in periodic and disordered dielectrical structures

Summary form only given. As demands on the speed of integrated optical devices increase, ever-shorter light pulses will be used in those devices. As the development of the photonic devices advances, so to will the need to monitor the behavior of short pulses as they propagate through such devices. However, peeking inside a photonic structure is far from trivial as conventional microscopy is limited by the diffraction limit. Recently, we demonstrated a non-invasive technique based on an optical photon scanning tunneling microscope (PSTM) that can be used to visualize pulses as they propagate through an optical device with both temporal and spatial resolution. With this technique we have now been able to observe the time-resolved motion of a short optical wave packet.

Tracking fs light pulses in space and time through advanced photonic structures

The propagation of short light pulses through advanced photonic structures like photonic crystals is influenced by the interplay of various physical mechanisms, for instance by the strong material dispersion and the low group velocity. To study the complex interplay between different mechanisms as pulses propagate through a structure, local time-resolved measurements are crucial.

Direct visualization of pulse propagation with near-field microscopy

Summary form only given. For the first time, the propagation of femtosecond laser pulses has been directly visualized with a time-resolved photon scanning tunneling microscope. Both the group velocity and the phase velocity can be unambiguously and simultaneously determined.