Dual-modulation difference stimulated emission depletion microscopy to suppress the background signal

Stimulated emission depletion (STED) nanoscopy is one of the most well-developed nanoscopy techniques that can provide subdiffraction spatial resolution imaging. Here, we introduce dual-modulation difference STED microscopy (dmdSTED) to suppress the background noise in traditional STED imaging. By applying respective time-domain modulations to the two continuous-wave lasers, signals are distributed discretely in the frequency spectrum and thus are obtained through lock-in demodulation of the corresponding frequencies. The background signals can be selectively eliminated from the effective signal without compromise of temporal resolution. We used nanoparticle, fixed cell, and perovskite coating experiments, as well as theoretical demonstration, to confirm the effectiveness of this method. We highlight dmdSTED as an idea and approach with simple implementation for improving the imaging quality, which substantially enlarges the versatility of STED nanoscopy.