Fig. 4: Setup and principle of ExPAN. | npj Imaging

Fig. 4: Setup and principle of ExPAN.

From: High contrast fluorescence polarization microscopy through double tagged photoswitchable fluorescent proteins

Fig. 4

a Setup. Like in conventional FPM (Fig. 1), the excitation polarization in a wide-field fluorescence microscope (blue beam with blue arrows) is rotated at a fixed frequency using, for example, a λ/2-wave plate (WP). In ExPAN, however, an additional wide-field deexcitation beam (orange beam) is rotated with a polarization always perpendicular to the excitation beam (orange arrows), resulting in much narrower modulation signals. b, c Modulation signals from a single molecule without (b) and with (c) ExPAN beam18.

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