Experimental investigation of recoil-momentum-generation efficiency under near-IR femtosecond laser ablation of refractory metals in vacuum

The use of ultrashort laser pulses is a way to increase recoil momentum under laser ablation of materials, because, in this case, the energy deposition per unit volume of the target material is substantially higher due to reduced heat dissipation. By using methods of combined interferometry, we estimated the specific impulse (～200–900 s), momentum coupling coefficient (～2 × 10^?5?3 × 10^?4 Ns/J), laser-energy conversion efficiency to kinetic energy of the gas-plasma flow (～0.05–0.82), and degree of the gas-plasma flow monochromaticity (～0.72–0.92) under femtosecond (τ ～ 45 fs, λ ～ 800 nm) ablation of refractory metals (Ti, Zr, Mo, and Nb) in vacuum.