A photothermal technique for ultra-high resolution measurements of thermal diffusivity of liquid mixtures was developed. Frequency scan experiments using the thermal-wave resonator cavity (TWRC) method [1] were performed. A theoretical model describing the one-dimensional temperature field within the cavity was developed. Comparison between the theoretical and experimental data for signal amplitude and phase in water shows excellent agreement. To achieve the ultra-high sensitivity of the measurements for liquid mixtures at low concentrations we modified the thermal-wave resonator cavity method coupling it with a signal common-mode rejection demodulation (CMRD) scheme [2]. This non-conventional technique has shown sensitivity of the photothermal signal to methanol in water at the level of 0.25% by volume.
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