Plasma Properties of 532 nm Laser-Ablated Aluminum E414d Target with Different Power Densities

Optical emission spectra of the plasma generated by a 532 nm Nd:YAG laser irradiation onto a standard aluminum alloy (E414d) was recorded and analyzed. The electron temperature was determined using the Boltzmann plot method with three aluminum spectral lines at 236.71 nm, 257.509 nm and 308.215 nm, whereas the electron density was inferred by measuring the Stark broadening line profile of Al(II) 281.619 nm. The experimental results confirmed that the local thermodynamic equilibrium was valid and the plasma was optically thin. The spectral line intensity increased initially with the increase in laser irradiance and saturated at higher irradiance levels. Results showed that the energy losses due to the reflection of laser beam from the plasma itself were insignificant. The absorption in the plasma through inverse bremsstrahlung and two-photon ionization were studied. At the same time, the variation of transition probability ratio of Al(I) 309.28 nm to Al(I) 308.21 nm with laser power density was also studied.