Numerical Simulations on Laser-Ablative Micropropulsion with Short and Ultrashort Laser Pulses

Kurzfassung

Aiming for the generation of high-precision thrust in the µN range, focused high-intensity laser pulses are used employing the recoil of the jet of the ablated material. Whereas a single laser pulse yields an extremely low impulse bit in the range of several nNs, a broad thrust range can be accessed by the variation of the laser pulse repetition rate up to several hundreds of kilohertz. A detailed laser parameter study is carried out for aluminum and gold as propellant varying the pulse length from 100 fs to 10 ns and the fluence from 0.09 to 23.8 J/cm^2. Two different regimes of thruster operation with respect to laser pulse length and specific impulse are identified. Irrespective of the pulse length regime, optimum impulse coupling is found at laser spot fluences around 2 J/cm^2 for aluminum and 20 J/cm^2 for gold, respectively, with coupling coefficients in the range of 25 to 40 μN/W. For ultrashort pulses, jet velocities are rather small yielding a specific impulse in the range of 70 s to 200 s, whereas for longer pulses beyond ≈ 100 ps, Isp is found to be in the range of 500 to 1000 s and beyond enabling low propellant consumption. However, ultrashort-pulse laser ablation might be favorable since material can be removed very smoothly which might contribute to very low thrust noise.