Label-Free Super-Resolution Imaging Using Non-Linear Exogenous Photon Avalanche Backlight

Optical imaging beyond the diffraction limit of light enables direct investigation of the structure, organization and functioning of sub-micrometer, highly transparent objects such as subcellular components, thin films and nano-engineered devices. However, most existing super-resolution optical techniques rely on fluorescent labels, which can alter sample properties, suffer from phototoxicity and photobleaching, and require complex instrumentation. At the same time, alternative label-free super-resolution methods remain technically complex, demanding, costly and often difficult to implement. Here we propose and experimentally demonstrate a new concept of label-free super-resolution optical imaging termed transmission avalanche backlight (TAB) microscopy. TAB microscopy exploits strong optical nonlinearities in exogenous photon-avalanche materials, which act as a far-field created, luminescent backlight forming a near-field virtual, fluorescent nano-aperture. Weak attenuation and scattering by highly transparent samples are translated into strongly amplified luminescence modulation of the avalanche backlight substrate, resulting in enhanced image contrast. Using a single-beam laser-scanning configuration, TAB microscopy achieves far-field, reconstruction-free imaging with optical resolution of approximately 180 nm. This approach provides a relatively technically simple, label-free route to sub-diffraction imaging and may complement existing techniques across biology, materials science, nanophotonics and nanoengineering.