Laser-plasma coupling for enhanced ablation of GaAs with combined femtosecond and nanosecond pulses

Abstract

The laser-plasma interactions that occur during the ablation of solid materials by a femtosecond filament superimposed with a lower-intensity nanosecond pulse are investigated. Pulses of 50 fs duration with intensities of ∼10¹⁴ W/cm² centered at 800 nm are combined with 8 ns pulses at 1064 nm with ∼10¹⁰ W/cm² intensity with delays of ±40 ns on crystalline GaAs targets in air. For each delay, the volume of material removed by a single femtosecond-nanosecond dual-pulse is compared to the laser-plasma interactions that are captured with ultrafast shadowgraph imaging of the plasma and shockwave generated by each pulse. Sedov-Taylor analysis of the shockwaves provides insight on the coupling of energy from the second pulse to the plasma. These dynamics are corroborated with radiation-hydrodynamics simulations. The interaction of the secondary pulse with the pre-existent plasma is shown to play a critical role in enhancing the material removal.