https://doi.org/10.1007/s100530050310
Far-field fluorescence microscopy with repetitive excitation
High Resolution Optical Microscopy Group, Max-Planck-Institute for Biophysical
Chemistry 37070 Göttingen, Germany
Received:
3
December
1998
Published online: 15 June 1999
We introduce the concept of repeatedly exciting an excited state of a photostable
fluorescent entity to generate a nonlinear fluorescence signal which is
solely based on the linear susceptibility of the molecule. The excitation
cycle between the fluorescent state 
and another state prolongs the average
lifetime of , with emphasis on those molecules that are in the center of
the focus. The photons emitted by the long-lived molecules in the center
are recorded by a temporal filter and constitute fluorescence that depends
nonlinearly on the excitation intensity. Theoretical analysis reveals that
this concept can provide three-dimensional imaging and improve the spatial
resolution in far-field fluorescence microscopy. We show that despite the
presence of diffraction the effective focal waist can in principle be narrowed
down to the molecular scale at the expense of signal.
PACS: 42.90.+m – Other topics in optics / 42.30.-d – Imaging and optical processing / 42.65.-k – Nonlinear optics
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999
