Enhanced fluorescence signal in nonlinear microscopy through supplementary fiber-optic light collection.

Nonlinear microscopy techniques crucially rely on efficient signal detection. Here, we present a ring of large-core optical fibers for epi-collection of fluorescence photons that are not transmitted through the objective and thus normally wasted. Theoretical treatments indicated that such a supplementary fiber-optic light collection system (SUFICS) can provide an up to 4-fold signal gain. In typical in vivo imaging experiments, the fiber-ring channel was brighter than the objective channel down to 800 microm depth, thus providing a gain >2. Moreover, SUFICS reduced noise levels in calcium imaging experiments by about 23%. We recommend SUFICS as a generally applicable, effective add-on to nonlinear microscopes for enhancing fluorescence signals.