Laser energy partitioning in nanosecond pulsed laser-induced air breakdown: effect of incident laser energy

Air breakdown is generated by a 1064 nm nanosecond pulsed laser beam, and laser energy deposited in the break-down (Ed), transmitted through the plasma region (Et) and carried away by the shock wave (Es) is estimated for the incident laser energy (Ei) range of 60-273 mJ. The Ed is approximately 85% of Ei at 60 mJ, rapidly increasing to 92% at 102 mJ. The shock wave front velocity and radius are measured as a function of Ei and propagation dis-tance. The shock wave velocity nicely follows the v & PROP; E0.3 i trend predicted by the laser-supported detonation wave model. The Sedov-Taylor theory is used to estimate Es, which rapidly increases with Ei, but Ei to Es conversion linearly decreases from 83% to 48%. At lower values of Ei, most of the laser energy is carried away by the shock wave, whereas the laser energy used in plasma heating or released in the form of electromagnetic and thermal radi-ation becomes important at higher laser energies. This implies that laser energy partitioning is highly dependent on the value of incident laser energy. These findings provide important insights into the fundamental physics of air breakdown and will be useful in a variety of applications such as laser-induced breakdown spectroscopy, laser ignition, and laser propulsion. & COPY; 2023 Optica Publishing Group