Thermometry of liquid water through slow light imaging spectroscopy

This work presents the first, to the best of our knowledge, experimental demonstration of slow light imaging spectroscopy for thermometry of liquid water. This novel technique for measuring temperature relies on detecting the spectral shift of Brillouin peaks in water using the temporal delay through a cell containing an atomic vapor. Stand-off sensing capabilities are achieved by time-domain measurements of Brillouin scattering tuned to be near a rubidium atomic resonance and passed through a cell filled with rubidium vapor. An injection seeded optical parametric oscillator (OPO) is demonstrated to be a versatile light source for slow light imaging spectroscopy applications. The narrow OPO pulse spectrum allows for a precise profiling of slow light features of rubidium and accurate tracking of the temperature dependence of Brillouin scattering spectral shift. A comparison between the experimental data and numerical simulation over a temperature range of 20 to 99 degrees Celsius shows a good agreement for both qualitative and quantitative results.