Measuring the refractive index in a wave excited in water by a laser pulse

The problem of measuring the refractive index in a spherical wave using the Toepler method with a two-sectional photodetector is considered. A technique for determining the width and amplitude of a wave perturbation from the measured time dependence of a schlieren signal is presented. It is shown experimentally that when a water surface is irradiated with an HF-laser pulse (the pulse energy is 50 mJ, the duration is 60 ns), an elastic wave with a width of ~2 mm and an amplitude that is inversely proportional to the travelled distance is excited. The minimum recorded value of the refractive-index gradient is ~3 × 10–8 mm–1; the absolute measurement error of the refractive index is 1.5 × 10–8. The obtained sensitivity and accuracy exceed the results that were previously published. The proposed approach is characterized by the extreme simplicity of the equipment, as well as by the easiness of the experimental implementation and processing of the measurement results.