Fluorophore discrimination by tracing quantum interference in fluorescence microscopy

We show fluorescence-detected quantum interference in a microscope setup and demonstrate selective enhancement or suppression of fluorophores using femtosecond pulse-pair excitation with periodic modulation of the interpulse phase.

Figure 1

(a) Experimental setup; the scanning mirrors and confocal detection schemes are not shown for simplification. (b) Relevant absorption spectral profiles (lines) of rhodamine-6G in ethanol (solid black) and fluorescein in basic ethanol (dashed red); data were taken from the web resource for spectral database [34] and presented after smoothing over adjacent points. The inset shows the pulse spectra (solid blue).

Figure 2

Fluorescence interferogram (QI signal) for rhodamine-6G (middle panel, black circles) and fluorescein (lower panel, red triangles) compared with optical field oscillation (upper panel, blue squares) for three different pulse-pair delay regions: ∼0 fs delay (left panel), ∼−100 fs delay (middle panel), and ∼−200 fs delay (right panel). The concurrent enhancement of rhodamine-6G fluorescence and suppression of fluorescein fluorescence at a definite interpulse time delay is also marked (dashed green oval).