Temperature dependence of photoacoustic and/or pyroelectric signal from solutions dispersed with ultra fine particles

In our photoacoustic system, a transparent photoacoustic cell is made where a modulated laser beam penetrates into a cell from one end to irradiate solution in the cell and reaches at the piezoelectric transducer attached to the other end of the cell. The amplitude and phase of the signals from several kinds of solution are measured as a function of modulation frequency and temperature. Solutions examined are pure water, water including ultra fine particles, solution of Na₂HPO₄ in water and solution including ultra fine particles. Existence of solute or fine particles reduces the amplitude comparing with that from pure water. In addition, ultra fine particles diluted in the solution are found to enhance the change of the signal due to the phase transition accompanied with the temperature change. In this way, it becomes easy to detect signals from transparent solutions by using this cell. It is found that easy detection is due to the simultaneous use of a pyroelectric and the photoacoustic effects.