Fast photothermal spatial light modulation for quantitative phase imaging at the nanoscale

Abstract Spatial light modulators have become an essential tool for advanced microscopy enabling breakthroughs in 3D, phase, or super-resolution imaging. However, continuous spatial-light modulation without diffraction artifacts, polarization dependence, and able to capture sub-ms microscopic motion is challenging. Here we present a photothermal spatial light modulator (PT-SLM) enabling the fast wavefront shaping free of diffraction artifacts, having a high transmissivity and modulation efficiency independent of light polarization. It is based on the microscopic heating of a thin layer of thermo-optic material confined between the photothermal heat-source and a transparent heatsink. We achieve a phase-shift > π with a response time as short as 70 µs with a theoretical limit in the sub-µs range. The combination of the PT-SLM with an interferometric scattering microscope (iSCAT) allowed us to perform quantitative phase imaging of sub-diffractional scatterers and decipher the 3D nanoscopic displacement of microtubules matching closely with control data from atomic force microscopy.