New modes in label-free super resolution based on photo-modulated reflectivity.

The recent advances in far-field super-resolution (SR) microscopy rely on, and therefore are limited by the ability to control the fluorescence of label molecules. We demonstrated a far field label-free SR methodology that relies on the nonlinear response of the reflectance to photo-modulation by a pump laser. Here we extend our approach in two directions. We show that the method can be further simplified and improved by using a single beam rather than a pump and probe or by adding spatial probe modulation to improve resolution. Additionally, we demonstrate SR in sectioning and further investigate the dynamics of non-linearity in photo-modulated reflectance. These new modalities of nonlinear photo-modulated reflectivity (NPMR) enhance its applicability using lower orders of nonlinear response.