Heterochromatic Nonlinear Optical Responses in Upconversion Nanoparticles for Super?Resolution Nanoscopy

Point spread function (PSF) engineering of the emitter can code higher spatial frequency information an image to break diffraction limit but suffer from complexed optical systems. Here we present a robust strategy simultaneously achieve diverse PSFs upconversion nanoparticles under single doughnut-shape scanning beam. By saturating four-photon state, high-frequency be extracted through doughnut emission PSF. In contrast, complementary lower carried out by Gaussian-like PSF, as result over-saturated at two-photon state. With Fourier domain heterochromatic fusion, verify capability synthesised PSF cover both low and information, yielding overall enhanced quality. We show resolution 40 nm, 1/24th excitation wavelength. This work suggests new scope for developing nonlinear multi-colour emitting probes improve quality noise control in nanoscopy.