Ultimate sensing resolution of water temperature by remote Raman spectroscopy.

The limit of sensing resolution of water temperature by remote Raman spectroscopy was investigated experimentally. A remote Raman spectrometer, which employed a telescope of 20 cm in pupil size and the second harmonic generation (SHG) of a Q-switched Nd:YAG laser, was used for the measurement. By analyzing the broad O-H stretching Raman band located near 3500  cm⁻¹, a parameter which is in second-order polynomial relation with water temperature from 13°C to 50°C could be obtained. The resolution of our remote Raman temperature sensor was better than ±0.2°C with measurement time shorter than 10 s. The influence of the Raman signal's signal-to-noise ratio on the resolution and salinity effect on the accuracy of temperature sensing were also investigated.