Quantitative Measurements of Ablative Laser Propulsion Parameters of Metal Foils Using Pulsed Nd:YAG Laser

Recoil momentum due to ablated products in the laser ablation process is the dominant source of thrust generation. The total momentum comprises the laser-supported shock wave in background gas and the momentum due to material flow. Based on experimental studies, the dependence of laser ablation propulsion parameters of metal foils has been investigated in atmospheric air. A Q-switched Nd:YAG laser operating at fundamental (1064 nm) and second harmonics (532 nm) is used to irradiate the target. Each sample's ablation is performed over a range of laser fluence values (106 to 107 J/cm2), which is achieved by varying the incoming laser energy per pulse and adjusting the focused beam spot diameter. The results obtained from these studies showed that the laser ablation propulsion parameters are influenced by laser parameters. Moreover, the target properties also plays significant role in calculating propulsion parameters which vary with wavelength. The highest Cm is obtained for Cu irradiated with 2.2 × 10–4 Ns/J laser pulse using fundamental harmonics at low laser fluence up to 1.5 × 106 J/cm2while at the highest fluence Fe gives higher Cm 1.810–4 Ns/J because of the difference in the physical properties of metal foils. As expected, changing the energy per pulse of the laser also affects the laser ablation propulsion efficiency. The Isp for Fe is highest for both harmonics i-e 41,675 s and 3490 s, respectively. The reason behind this is that the optical properties of Fe vary by changing wavelength. Such higher Isp is required for long-range missions, so Fe proved to be the best propellant.