Femtosecond and picosecond laser microablation: ablation efficiency and laser microplasma expansion

Laser ablation efficiency and plasma plume expansion were studied using the interaction of Ti-Al2O3 laser pulses (wavelength 800 nm; energy 20 μJ; mode TEM00; waist diameter 11 μm; pulse durations 70 fs, 150 fs, 0.4 ps, 0.8 ps, 2 ps, and 10 ps) with copper in air. A moderate laser pulse energy of 20 μJ was used to eliminate the sharply focused femtosecond laser beam disturbance caused by its nonlinear interaction with air. The craters formed at the surfaces were measured with 0.1 μm longitudinal and 0.5 μm transverse resolution. Laser plasma expansion was measured by an ICCD camera with 3 μm spatial and 1 ns temporal resolution. These measurements were performed in a time delay range of 0–50 ns.