Revealing the influence of solvent polarity and refractive index on whispering gallery mode-based laser sensors.

Whispering-gallery-mode (WGM) lasers are highly sensitive sensing tools in solution-based environments, but their performance is influenced by multiple factors, leading to complex spectral shifts. In this study, we decode the influence of solvent polarity on the WGM laser sensors, exploring its interaction with solvent refractive index (RI) in optofluidic systems. A binary polarity solvent of ethanol (EtOH) and ethylene glycol (EG) containing rhodamine 6G (Rh6G) is utilized as the lasing gain medium. Experimental results indicate that increasing solvent polarity induces a redshift in the lasing wavelength, while rising RI lowers the quality factor (Q-factor), causing a competing blueshift. These opposing effects collectively impact the overall performance of the sensors. Based on these observations, we propose a predictive framework for optimizing WGM laser sensors across different Q-factor levels, offering valuable insights for sensor design and fabrication.