Angular distribution of ions produced by laser ablation of magnesium with special reference to sublimation energy

A 99.99% pure Mg target was irradiated with 100 shots of a Q-switched pulsed Nd:YAG laser (1.064 μm, 9 ns, 1.1 MW) in a vacuum ∼10−3 mbar to generate ions from laser-produced plasma (LPP). CR-39 detectors were positioned at 0°, 30°, 60° and 90° with respect to the normal of the target surface. The LPP Mg ions made tracks on the detectors, which were then etched in 6 N NaOH solution for 8 h at 70 ± 1 °C. The etched detectors were then analyzed using computer controlled Motic DMB series optical microscope. It is found that the Mg ions with maximum energy and maximum flux were obtained at an angle 0° with respect to the normal of the target surface, whereas both energy and flux of the ions decrease with the increase in angle. The angular distribution of Mg ions is encompassed by a cosine power-law in which the exponent n of the cosn θ distribution is found to be 0.24. This together with the wealth of data (n = 3-24) obtained by Konomi et al. (2009) for 11 different metals has been shown to follow a linear relationship between the exponent n and the sublimation energy of target metals.