Thrust and plasma dynamics of multi-walled carbon nanotube paper under femtosecond laser ablation

Laser ablation propulsion is a promising micro-propulsion method for microsatellites, and carbon nanotube paper (CNTP) offers potential in this area. Here, we investigate the propulsion performance and plasma dynamics of multi-walled CNTP (M-CNTP) ablated by femtosecond laser pulses (35 fs, 800 nm, 1 kHz). Within a power range of 58-128 mW, thrust increases linearly from 3.8 ± 0.2 μN to 6.2 ± 0.3 μN, while the impulse coupling coefficient (C_m) increases slightly, followed by decreases, with maximum 66.9 ± 3.74 µN/W at 62 mW. SEM and Raman analyses show that ablation exposes CNT tips without changing the I_D/I_G ratio, indicating a non-thermal mechanism. High-speed imaging reveals a radially expanding plasma plume from the first pulse; under multi-pulse irradiation, ejecta accumulate along the beam path, triggering secondary plasma and a two-stage velocity decay. Spherical plasma structures, including hole-through plumes upon target penetration, are observed. The C_m reduction is primarily attributed to plume absorption and reverse-plume effects. This work elucidates the energy transfer mechanisms during femtosecond laser interactions with M-CNTP and provides experimental insights into improving the efficiency of pulsed laser propulsion.