Thrust performance of pulsed-laser ablation impulses for wavelengths of 1064 nm and 532 nm

Space propulsion using pulsed-laser ablation of metals is a promising technology, particularly for deorbiting space debris or satellites at the end of life. The momentum coupling coefficient, a key parameter in this technology, depends on the incident laser wavelength. Although former studies have evaluated this dependency, they often overlooked the influence of variations in beam profiles. A method to estimate the local momentum coupling coefficient based on beam profiles was previously demonstrated using a nanosecond laser with a wavelength of 1064 nm. In this study, the local momentum coupling coefficient for a wavelength of 532 nm was estimated for the target materials of pure aluminum, extra-super duralumin, and oxygen-free copper using the same method and compared with that of the 1064 nm reported in the previous study. The comparison revealed that the local momentum coupling coefficient displays similar trends across materials for both wavelengths, except for oxygen-free copper, which exhibited a significantly higher ablation threshold for the wavelength of 1064 nm. The two important parameters for space propulsion, namely, the specific impulse and thrust efficiency, were also derived for both wavelengths based on the impulse and reduction mass of an ablation target. The specific impulse showed a weaker dependency on wavelength, with values ranging from approximately 2700 to 3100 s for pure aluminum, 2300–2600 s for extra-super duralumin, and 1500–2000 s for oxygen-free copper. These results are consistent with the tendency reported in a previous study that materials with a lower mean atomic weight yield higher specific impulse. In contrast, thrust efficiency clearly varied depending on material and wavelength, being approximately 40 %, 36 %, and 21 % at λ = 532 nm, and 32 %, 31 %, and 12 % at λ = 1064 nm for pure aluminum, extra-super duralumin, and oxygen-free copper, respectively. These findings provide valuable insights into the wavelength dependency of laser ablation thrust performance and its implications for space propulsion systems.