The fundamental determining factor of angular emission of multiple charged ions ejected by laser ablation of different metals and their binary alloys

Ions up to ionization state q = 4, emitted from laser produced plasma of Al, Ti, Ti50Al50 and Ti75Al25 targets ablated by Srivastava et al. (2006), are distributed angularly in the form of a cone, and for each ionization state the angular distribution has been shown to follow the cosine power-law: F = Focosnθ. It is found that the value of exponent n of cosnθ distribution function increases with the increase in ionization state. For each target, the value of exponent n of individual ionization states as well as total charge exhibits an excellent linear correlation with the room temperature Debye–Waller thermal parameter B or the mean-square amplitude of the atomic vibrations of the targets. It is further reported that the FWHM of ion distribution with Gaussian function fitting done by Srivastava et al. (2006) also depends linearly on B rather better than its dependence on the atomic mass of pure metal targets or average atomic mass in the case of their binary alloy targets. The FWHM of ion distribution for Al, Ti, Cu, Mo, W and their alloys Ti25Al75, Ti34Al66, Ti50Al50, Ti75Al25, W60Cu40, W80Cu20, W90Cu10 and Mo70Cu30 laser ablated by Srivastava and Rohr (2005) are also found to have much better correlation with the room temperature Debye–Waller thermal parameter B as compared to the atomic mass of the target.

► Both cosine power-law and Gaussian function can be employed to describe the angular distribution of LPP ions. ► Laser ablation parameters have the best correlation with the room temperature Debye–Waller thermal parameter B. ► Crystalline materials, whether metals or alloys, possess lattice-vibration memory in the plasma state.