We report the laser irradiation-induced oxidation of bismuth metal investigated in situ by micro-Raman spectroscopy as a function of irradiation power and time. The purely optical synthesis and characterization of β-Bi_2O_3 oxide microislands on metallic Bi surfaces is shown to be stable over time, even at room-temperature. By closely examining possible reactions on simple Bi morphologies it is revealed for the first time that the ensuing oxide phase is critically dependent on the final oxide volume and follows a fixed kinetic transformation sequence: 32O_2(g)+2Bi(l)→β–Bi_2O_3(s)→α–Bi_2O_3(s). These findings are unusual within the framework of traditional Bi_2O_3 thermal transformation relations. An electrostatic mechanism involving a changing Bi_2O_3 surface-to-volume ratio is proposed to explain the room-temperature metastability of small β-Bi_2O_3 volumes and the subsequent transformation sequence, as well as unifying the results of previous studies.