Title: Saturated absorption competition microscopy,
Abstract: We introduce the concept of saturated absorption competition (SAC) microscopy
as a means of providing sub-diffraction spatial resolution in fluorescence
imaging. Unlike the post-competition process between stimulated and spontaneous
emission that is used in stimulated emission depletion (STED) microscopy, SAC
microscopy breaks the diffraction limit by emphasizing a pre-competition
process that occurs in the fluorescence absorption stage in a manner that
shares similarities with ground-state depletion (GSD) microscopy. Moreover,
unlike both STED and GSD microscopy, SAC microscopy offers a reduction in
complexity and cost by utilizing only a single continuous-wave laser diode and
an illumination intensity that is ~ 20x smaller than that used in STED. Our
approach can be physically implemented in a confocal microscope by dividing the
input laser source into a time-modulated primary excitation beam and a
doughnut-shaped saturation beam, and subsequently employing a homodyne
detection scheme to select the modulated fluorescence signal. Herein, we
provide both a physico-chemical model of SAC and experimentally demonstrate by
way of a proof-of-concept experiment a transverse spatial resolution of
~lambda/6.