Whispering gallery mode sensor for phase transformation and solidification studies

Whispering gallery mode (WGM) sensors are created by coupling a dielectric microresonator with the evanescent field of an optical fiber. Since the sensor is created by two separate entities, most of the existing studies are limited to using them in fluid environments, such as air or water, for the ease of manipulation and placement in the optimum configuration. This work is focused on studying the possibility of using WGM sensors inside a solid material. The sensor is immersed in water, which is cooled to solid state and the sensor survival is monitored. In subsequent studies, three remelting cycles are carried out and temperature measurements are obtained through the sensor. The sensor output is calibrated with the temperature data obtained from a thermocouple. The results show that a linear relationship exists between temperature and WGM shift, which enables application of these sensors in temperature measurement.Considering that the sensitivity of WGM sensors is very high (10^-6N force and 10^-5K temperature), they can be used for high resolution studies on solidification in cryogenic environments.