Superconcentration of light: circumventing the classical limit to achievable irradiance

Concentration of light is limited by a fundamental physical principle, which ensures that étendue, the product of area and solid angle, can never decrease in an optical system. In microscopy, many superresolving methods, which can overcome the classical resolution limit, have recently emerged. We propose, and demonstrate experimentally, that it is also possible to circumvent the classical light concentration limit. Actually, most superresolution methods exhibit a common drawback: with respect to the total number of emitted photons, they are less efficient than standard widefield microscopy. Most methods "shave"' the point spread function (PSF) by discarding the disturbing signal from its edge. We show, that in contrast to PSF-shaving, methods related to reassignment microscopy (image scanning microscopy, optical photon reassignment, rescan confocal, instant structured illumination microscopy) concentrate all detected photons in their superresolving images and thereby increase the detected signal per sample area compared to widefield microsopy. We term this behavior superconcentration, as it breaks the classical light concentration limit.