3.5. Optoacoustic setup
OA measurements were performed using the experimental setup illustrated in Fig. 2a. For the generation of OA signals in the medium under study, the radiation of the second harmonic (λ = 532 nm) of a pulsed Nd:YAG laser (a Solar LQ129, Belarus) was used. The laser pulse duration τL = 22 ns at the 1/e level, which was measured with a photodiode. The laser pulse energy could be varied with a number of neutral filters and did not exceed 1 mJ and the corresponding laser fluence did not exceed few mJ cm−2. The laser radiation propagated through the system of a light scatterer and a convex lens to homogenize light distribution in the beam cross-section and make the beam diameter 12 mm at the surface of the medium under study. The laser pulse repetition rate was 50 Hz, which allowed us to register OA signals in 3 s (at 128 signal averages) and thereby neglect any signal changes related with chemical reactions inside the OA cell.