High-resolution Collinear Chiral Sum Frequency Generation Microscopy by   Using Vectorial Beam
  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. 
Ziheng Ji, Wentao Yu, Hong Yang, Kaihui Liu, Qihuang Gong, Zhiwen Liu,   Kebin Shi
physics.optics physics.bio-ph