Tuning liquid whispering gallery mode microlasers by surface tension

Since the first realization of ruby laser in 1960s, the rapidly developed laser technology plays significant roles in modern research, industry as well as military. The cavity, which is the main component of a laser, attracts enormous research interests due to the variety of configurations and abundant applications in bio/chemical sensing, optical filters/switches, quantum information processing and nonlinear studies. Up to now, it is still challenging to engineer the resonant peaks in a single microcavity, especially in liquid environment, which hinder the development of microcavities in biomedical and fluidic avenue. In this work, novel dye-doped polymer quasi-disk microlasers are realized on water surface by employing a microplotter with inkjet printing technique. Detailed spectroscopy analysis reveals the whispering gallery mode (WGM) lasing mechanism of the microlasers with high quality factor. Notably, size of the microcavities can be easily tuned by modifying the surface tension of water by adding surfactant, thus tailoring the lasing wavelength. Detail studies show that the diameter change of the main WGM plane can reach an average of 40% and the corresponding lasing envelop shift can be up to 10 nm. Moreover, the shifting is demonstrated to be bidirectional and reconfigurable. In addition, high sensitivity and detectivity (19.85 THz/(mol · mL
⁻¹
) and 5.56 × 10
⁻³
mol · mL
⁻¹
, respectively) sensing of water-soluble organic compounds exemplified by ethanol is achieved. Our work not only demonstrates a new type of whispering gallery mode microlaser, but also launches a new approach to manipulate lasing peaks, which has significant potential applications in fluidic and bio-sensing.