Trapping and characterization of growing vaterite microparticles in an optical tweezer

Vaterite microparticles are ideal optical micromotors due to their relatively high birefringence and spherical shapes. The synthesis procedures of vaterite particles are still not mature. We report a technique to in-situ observe the growth process of vaterite microparticles using a single-beam optical tweezer. The instantaneous particle diameter can be retrieved from the high-resolution optical images collected with a high numerical aperture objective, and the particle birefringence can be inferred from the frequency of particle rotation when launching a circularly polarized trapping beam. The technique may be used to optimize the synthesis procedures of vaterite microparticles, which have vast ranges of applications on optical trapping, micromotors, and precision metrologies.