Title: Room-temperature Continuous-Wave Upconversion White Microlaser Using a Rare-earth-Doped Microcavity

Abstract: White laser covering the visible color spectrum is critical in various applications including vivid display, holographic imaging, and light-based version of Wi-Fi, but it is still challenging to realize a white microlaser due to the rigorous requirement for the balance between the optical gain and feedback in a wide wavelength range. Here, we employ thulium, erbium, and ytterbium elements corporately for the upconversion white lasing by an individual ultrahigh-quality (Q) (up to 10⁸) doped microcavity with microwatt thresholds for the red, green, and blue lasers. To the best of our knowledge, it is the first rare-earth-element-based room-temperature continuous-wave white microlaser. This microlaser also exhibits relatively stable chromaticity over 180 min, which makes it possible for practical applications.