Fig. 2

Comparison between polarization modulation (PM) and pSIM imaging. a The reciprocal space of PM microscopy, including the three harmonics. The zeroth harmonic determines the intensity of the image, while the phases of the first harmonics determine the dipole orientation. b The three directions of structured illumination result in six spatial first harmonics (blue), which make up the reciprocal space of pSIM together with the zeroth harmonic (red) and two angular first harmonics (yellow). c pSIM imaging results of SYTOX orange-labeled DNA filaments, with the dipole orientations being pseudocolored. The color wheel indicates the relationship between the dipole orientation and the pseudocolor. The dipole orientation of SYTOX orange is inserted perpendicularly into the DNA filament. The zoomed-in results in d, e compare the results of PM and pSIM imaging. f A histogram of the dipole orientations in c, where the angle represents the difference between the dipole orientation and the direction of the DNA filament. g, h Two simulated filaments with the dipole orientation tangential to the filament. Compared with the PM results (g), the pSIM results (h) simultaneously show the underlying structure and measure the dipole orientation. Scale bars: c 2 μm and d–h 200 nm