High spatial resolution collinear chiral sum-frequency generation microscopy

Chiral sum-frequency generation (SFG) has proven to be a versatile spectroscopic and imaging tool for probing chirality. However, due to polarization restriction, the conventional chiral SFG microscopes have mostly adopted noncollinear beam configurations, which only partially cover the aperture of microscope and strongly spoil the spatial resolution. In this study, we report the first experimental demonstration of collinear chiral SFG microscopy, which fundamentally supports diffraction-limited resolution. This advancement is attributed to the collinear focus of a radially polarized vectorial beam and a linearly polarized (LP) beam. The tightly focused vectorial beam has a very strong longitudinal component, which interacts with the LP beam and produces the chiral SFG. The collinear configuration can utilize the full aperture and thus push the spatial resolution close to the diffraction limit. This technique can potentially boost the understanding of chiral systems.