Spatiotemporal Microscopy: Shining Light on Transport Phenomena

Transport phenomena like diffusion, convection, and drift play key roles in the sciences and engineering disciplines. They belong to the most omnipresent and important phenomena in nature that describe the motion of entities such as mass, charge or heat. Understanding and controlling these transport phenomena is crucial for a host of industrial technologies and applications, from cooling nuclear reactors to nanoscale heat-management in the semiconductor industry. For decades, macroscopic transport techniques have been used to access important parameters such as charge mobilities or thermal conductivities. While being powerful, they often require physical contacts, which can lead to unwanted effects. Over the past years, an exciting solution has emerged: a technique called spatiotemporal microscopy (SPTM) that accesses crucial transport phenomena in a contactless, all-optical, fashion. This technique offers powerful advantages in terms of accessible timescales, down to femtoseconds, and length scales, down to nanometres, and, further, selectively observes different species of interest. This tutorial review discusses common experimental configurations of SPTM and explains how they can be implemented by those entering the field. This review highlights the broad applicability of SPTM by presenting several exciting examples of transport phenomena that were unravelled thanks to this technique. The diffusion, convection, and drift of particles and heat belong to the most ubiquitous and important phenomena in nature. In this review, the authors make a case for spatiotemporal microscopy - an optical technique that enables studying such transport phenomena with a powerful combination of high spatial and high temporal resolution, thus shining light on previously inaccessible transport phenomena.image