Researchers have a growing need to push optical microscopy beyond the diffraction limit to answer key questions in biology, and stimulated emission depletion (STED) has proven to be a fluorescence imaging technique that can accomplish this goal. Biologists are currently seeking to connect molecular behavior to macroscopic behavior, determining how cells signal with each other, and how signaling at the cellular/organism level is then relayed back to DNA/RNA level control to regulate single genes. A STED nanoscope uses two laser beams. The first is the excitation laser, which as in confocal microscopy is usually focused to a near-diffraction-limited spot within a fluorescently labeled sample. The excitation wavelength of this laser is chosen to match the absorption peak of the target fluorophore. When applying a high enough STED laser power above a certain threshold, all the excited fluorophores in the path of the STED beam emit at the STED wavelength making them unavailable for fluorescence.