Polarization state visualization measurement of near-infrared light based on the metasurfaces combining NaYF 4 : Yb 3+ /Tm 3+ upconversion nanoparticles

Near-infrared (NIR) light is of great importance for radar, stealth, and imaging applications. However, the polarization state of NIR light cannot be directly perceived by the naked eye, posing challenges for practical detection. Here, we demonstrate a strategy for visualizing NIR polarization states by integrating a reflective metasurface with NaYF 4 : Yb 3+ /Tm 3+ upconversion nanoparticles (UCNPs). The metasurface is designed with a polarization-dependent phase profile that generates two split fluorescence ring patterns under 980 nm excitation. By analyzing the intensity ratio between the two rings, the ellipticity and handedness of the incident polarization can be determined intuitively. Experimental results agree well with far-field diffraction simulations, confirming the feasibility of this approach. Our work provides a new route toward compact and visual NIR polarimetry using rare-earth-doped UCNPs and metasurfaces.