We introduce upconversion lasing of a rare-earth ion-doped fluorozirconate glass microsphere in which tensof-micrometer-sized, genuinely spherical glass particles are produced by a melting method and pumped by a focused near-infrared laser beam. Three-photon-excited emission can be observed in the blue and red wavelength regions at room temperature, and their pumping-power dependences indicate the lasing operation. We also discuss the application of the microspherical upconversion laser as a

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... be of a near-field scanning optical microscope. A nanometer-sized particle is attached to the lasing microsphere, which can scatter the highintensity evanescent field generated just outside of the sphere, resulting in the formation of a minute light source for use in near-field microscopy. The lasing microspherical probe has an advantage of high sensitivity due to intracavity enhancement of the tunneling loss.