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

Abstract

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.