Studies on laser defocusing effects on laser ablation inductively coupled plasma-atomic emission spectrometry using emission signals from a laser-induced plasma

The effect of laser defocusing on analytical performance of laser ablation inductively coupled plasma atomic emission spectrometry (LA-ICP-AES) was studied by varying laser focus conditions with respect to the surface of a low-alloy steel and a powdered sediment pellet. Laser-induced plasma (LIP) and LA-ICP-AES emission signals and LIP excitation temperatures (LIP Tex) were determined and compared for different laser defocus conditions. LIP Fe and LA-ICP-AES Fe emission signals and LIP Tex decreased when the laser was defocused for the low-alloy steel. On the other hand, when the sediment pellet was ablated, LIP Tex decreased when the laser was defocused. However, LA-ICP-AES Fe emission signals increased at first, then decreased when the laser was defocused more. It was concluded that LIP Tex and LIP and LA-ICP-AES Fe emission signals are dependent on laser shot conditions (focus–defocus), and are also dependent on sample type (texture, mineralogy, hardness, conductivity and heat capacity).