Laser power and wavelength dependence of alumina reduction using YAG laser ablation considering inverse bremsstrahlung

Abstract

Among the lunar surface regolith, alumina is confirmed to be present in about 10% in the whole moon, especially in the highlands about 23%, which is one of the representative substances. Although alumina itself is not a very versatile material, reduced aluminum has a lot of applications for future lunar activities including a base construction. The laser ablation is one of the promising reduction methods because it does not require reducing agency. In this study, alumina was reduced through YAG laser ablation and generated aluminum was collected using a copper plate. The collected aluminum mass was estimated by the volume of hydrogen gas evaporated in hydrochloric acid titration. Then, the reduction efficiency was estimated as the ratio of collected aluminum to the total ablated mass. They were investigated in terms of the variation of the three laser wavelengths: 355, 532 and 1064 nm. Besides as the experimental condition, the peak power, number of laser shots, and ambient pressure were set as 5–15 MW, 3000–12000 shots, and 1.0–600 Pa, respectively. As a result, we verified alumina reduction by observation of Al I, Al II, Al III spectra. Al mass of 0.34 mg and energy conversion efficiency of 13% were achieved in 355 nm and 9000 shots and 1.0 Pa.