Permanent alterations in a water-filled silica microcapillary induced by optical whispering-gallery modes

Silica and water are known as exceptionally inert chemical materials whose interaction is not completely understood. Here we show that the effect of this interaction can be significantly enhanced by optical whispering gallery modes (WGMs) propagating in a silica microcapillary filled with water. Our experiments demonstrate that WGMs, which evanescently heat liquid water over several hours, induce permanent alterations in silica material characterized by the subnanometer variation of the WGM spectrum. We use the discovered effect to fabricate optical WGM microresonators having potential applications in optical signal processing and microfluidic sensing. Our results pave a way for ultra-precise fabrication of resonant optical microdevices and ultra-accurate characterization of physical and chemical processes at solid-liquid interfaces.