Efficiency of recoil momentum generation during femtosecond laser ablation of copper in vacuum

Abstract

thrusters. Introduction. Increasing the effi ciency of recoil momentum generation during laser ablation of condensed media is crucial for the development of laser induced controlled thermonuclear fusion (1) and the development of laser-plasma thrusters (2). It is also important for the creation of gas-plasma fl ow injectors (3), technologies for direct laser-induced transport of matter (4), laser-plasma deposition of thin fi lm coatings (5), and the initiation of processes in micro-electromechanical systems (6). When laser radiation with an energy density (fl uence) exceeding the ablation threshold is incident on condensed materials, a gas-plasma fl ow is generated which is characterized by the number and velocity distribution of the particles drawn into the fl ow. When a metal is irradiated, the laser energy is absorbed in a thin (~10 -8 -10 -7 m) layer at the surface, so that the volume density of absorbed laser energy is high. The high thermal conductivity of metals means that this energy spreads into the depth of the material, with the size of the thermal interaction zone being proportional to the duration of the laser pulse (7). The velocity of the atoms and ions in the laser induced gas-plasma fl ow depends substantially on the fraction of the absorbed energy that is dissipated as heat (8).