Influence of Microscopic Crater Formation on Impulse Generated with Repetitive Pulsed Laser Ablation

Abstract

The relationship between impulse and crater formation on an Al ablator with repetitive irradiation of Nd:YAG laser pulses (wavelength of 1064 nm, pulse duration of 7 ns) is investigated. The mNs level impulse is measured in a vacuum by a torsion type impulse balance. Surface area changes caused by crater deepening are measured with a laser microscope, then used for calculating the effective fluence. The fluence is compared to a corresponding variation in the momentum-coupling coefficient with repetitive pulses. The impulse with repetitive pulses becomes undetectable because the effective fluence decreases to the ablation threshold. The momentum-coupling coefficient fits to a simple variation; that is, it sharply increases to a peak value as the effective fluence increases, then gradually decreases.