Energy partition in underwater nanosecond laser ablation

We investigated the conversion of optical energy into mechanical energy during nanosecond laser ablation in an underwater regime. Our study analyzed the energy distribution between the shockwave, cavitation bubble, and work done by plasma impulse on the solid target, while also examining how laser intensity and absorptive coating affect this distribution. We monitored the evolution of the shockwave and cavitation bubble using the photoelasticity imaging technique and a high-speed laser stroboscopic videography system in the photoelasticity mode. Based on the experimental data, we determined the energy allocated to each process. Our result showed that shockwave energy contributed the most to the energy balance, followed by the cavitation bubble energy. The ratio of shockwave energy to cavitation bubble energy was independent of the laser pulse energy. Coating material helps to convert more optical energy to the thermal energy of the plasma plume, thus increasing the overall optical-to-mechanical energy conversion efficiency.