We developed an original method for space- and time-controlled generation of localized regions of enhanced laser-induced mechanical waves deep beneath the surfaces of liquids and soft substrates with very promising results. We developed a Nd:YAG laser system capable of delivering the optimal inducive laser pulse parameters. Such a system is able to generate a sequence of high-energy synchronized laser pulses in duration of a few tens of nanoseconds with a delay between consecutive pulses in the range from 10 µs to 200 µs and the energy of an individual laser pulse in the range from 0.1 J to 2 J. It is coupled with a specially tailored optoacoustic lens. The development of the optoacoustic lenses was directed mostly at determining their optimal geometries, dimensions, and composition materials. We tested a variety of lenses with different surface curvature shapes and focal lengths as well as their combinations arranged in a particular matrix. As lens composition materials, we investigated different combinations of absorptive materials and materials with a large thermal expansion (carbon nanotubes, graphite, charcoal, polymer polydimethylsiloxane), and different metals (titanium, aluminium, copper). Experimentally, we used a high-speed camera (? 2 100 000 fps, ? 1024 x 1024 pixels) and a back-to-front nanosecond flash illumination of the substrate to study the spatial distribution of its deformation and destruction due to the transition of the laser-generated mechanical waves. An examples of a multi-pulse laser-generated ultrasound focusing in a certain subsurface region are presented.
COBISS.SI-ID: 16802075