Far-field super-resolution microscopy based on the nonlinear response of photothermal excitation

Far field Super resolution (SR) microscopy, based on the emission of label fluorescent molecules, has become an important tool in life sciences. We present a new, label free, far field SR scheme, aimed towards material science, which is based on ultrafast, nonlinear excitation of materials to non-equilibrium state. In a pump-probe scheme, we optically excite a spatial temperature profile throughout the diffraction limited spot, and probe the material with an overlapping beam. Due to nonlinearities in thermal properties, we demonstrate enhancement of at least x2 better than the diffraction limit. Our approach can be extended to include other temperature dependent physical properties such as Raman scattering, reflection/absorption edge or luminescence. The method is suitable to characterize semiconductor and optoelectronic systems in vacuum, ambient, and liquid, semi-transparent and opaque systems, ultrathin and thick samples alike. In this communication we present the method and discuss some major physical consideration and experimental aspects of its application. We focus the discussion on ultrafast dynamic and thermal properties. We also discuss the applicability of the method in the unique case of VO₂ where photo-induced phase transition provides the contrast and present a highly accurate optical edge detection method based on the modulation phase.