Efficiency of recoil momentum generation during femtosecond laser ablation of copper in vacuum

A combination of interferometric techniques is used to determine the specific impulse (~250–300 s), specific mechanical recoil momentum (momentum coupling, 1–3∙10–4 N∙s/J), efficiency with which the laser energy is converted to kinetic energy of the gas-plasma fl ow (~0.1–0.55), and degree of monochromaticity (~0.75–0.82) of the gas-plasma flow during femtosecond (τ ~ 45 fs, λ ~ 800 nm) ablation of copper in vacuum. The experimental results are compared with published data covering a wide range of laser interaction parameters.