Investigating crater formation in nanosecond laser ablation of aluminum foils

A nanosecond Nd:YAG laser was used to study the laser ablation of aluminum foil in the phase explosion regime at a laser intensity range of 0.63–3.61 ×1012W/cm2. Laser ablation and plasma characteristics were studied using microscopic ablation crater images, plasma emission spectra, and plasma plume images. Measured plasma density using a Stark width of Al I (396.2 nm) showed a strong linear correlation with crater size, with a Pearson correlation coefficient (r) of 0.97. To understand the origin of this linear correlation, plasma temperature was estimated using Bremsstrahlung emission from 512 to 700 nm. The estimated plasma temperature and aspect ratio of the plasma plume were negatively correlated, having r=−0.76. This negative correlation resulted from a laser-plasma interaction, which heated the plasma and increased its hydrodynamic length. The percentages of laser energy used for plasma heating (Ep/EL) and Al foil ablation (EAl/EL) were estimated from plasma temperature. Increased EAl/EL, such as crater size, with increasing laser intensity, confirms that greater mass ablation is the fundamental reason for the strong linear correlation between crater size and plasma density.