Nanopore tomography of a laser focus

We demonstrate that the ionic current through a solid-state nanopore can be used to measure at single nanometer resolution the three-dimensional intensity profile of a laser directly in the focus of a microscope objective. We find a linear dependence of the ionic current on the incident laser power since the laser-induced heat increases the temperature locally in the solution. Our data show a temperature increase of up to 20 K in the center of the focus for a laser wavelength of 1064 nm. Measurements of the two-dimensional temperature profiles at different positions along the optical axis allow us to reconstruct the three-dimensional temperature profile of the laser focus, similar to tomography. Our new technique does not rely on the help of any optical elements and allows quantitative measurement of optical intensity or temperature distributions in aqueous environments with nanometer resolution.