Laser-based measurement of temperature or concentration change at liquid surfaces

A noncontact laser-based thermoreflectance technique was presented to measure changes in temperature or concentration at a liquid surface. Changes in temperature and for multi-component liquid mixtures, concentration led to a change in the liquid index of refraction, altering the reflectivity of the liquid surface. Temperature variations in 1-propanol, methanol, ethanol, and water were measured with uncertainties of 0.5, 0.7, 0.7, and 3.7°C, respectively, while for binary mixtures, the concentration of a methanol-1-propanol mixture was measured with an uncertainty of 0.3%. Keeping the beam angle of incidence near 0° minimized beam deflection due to surface deformation. Accurate high-spatial-resolution temperature information was critical for high purity and low-defect crystals.