Photothermal dielectric effect with liquid

A new photothermal technique for measuring the thermal characteristics of a liquid is proposed. This is based on the temperature characteristic of the dielectric constant of light-irradiated liquid. When an alternating temperature change occurs in a liquid material due to the absorption of chopped light, an alternating variation of capacitance is caused due to the temperature characteristic of dielectric coefficient of the liquid and this variation is detectable with sufficient dynamic range and sensitivity using a frequency demodulation technique. Quantitative derivations are presented for the alternating capacitance variation in terms of the optical, thermal, dielectric and geometric parameters of the system. The experimental results for ethyl alcohol are shown to be in good agreement with theoretical ones.