  In chiral sum frequency generation (C-SFG), the chiral nature of
${\chi}^{(2)}$ requires the three involved electric fields to be pairwise
non-parallel, leading to the traditional non-collinear configuration which is a
hindrance for achieving diffraction limited resolution while utilizing it as a
label-free imaging contrast mechanism . Here we propose a collinear C-SFG
(CC-SFG) microscopy modality by using longitudinal z-polarized vectorial field.
Label-free chiral imaging with enhanced spatial resolution (~1.4 times
improvement in one lateral and the longitudinal directions over the traditional
non-collinear scheme) is demonstrated, providing a new path for SFG microscopy
with diffraction-limited resolution for mapping chirality.
