Super-Resolution Photothermal Imaging at the Microscale by Model-Based Image Reconstruction

Super-resolution strategies expand the applicability of imaging modalities toward previously inaccessible spatial scales. Herein, photoactivated far-infrared thermography is pushed from the millimeter to the micrometer scale by a 2D super-resolution imaging approach capable of tackling the resolution barriers imposed by both diffraction-limited signal collection and lateral spatiotemporal heat diffusion. The proposed imaging strategy relies on a full-wave forward model of far-infrared thermography and on an image-inversion approach, which reconstructs the surface distribution of the sample photothermal absorbers via gradient-descent optimization as the one yielding the best match between predicted and experimental images. With minute-long acquisitions on a commercial low-cost far-infrared camera, less-than-5 μm spatial resolution is demonstrated on both synthetic samples and human liver biopsies ex vivo, thereby exemplifying the applicability of super-resolution photothermal imaging to the fast nondestructive characterization of biological specimens well below the tissue spatial scale.