Optical restriction of plasma emission light for nanometric sampling depth and depth profiling of multilayered metal samples.

Improvement in depth profiling capabilities of laser-induced breakdown spectrometry (LIBS) for multilayered samples has been attempted. For this purpose, in a typical LIBS experiment, an optical restriction consisting of a pinhole placed between the dichroic mirror and the collecting lenses has been used. This new optical approach allows observing only the light emission coming from the central region of the plume. The microplasma was created on the sample by a pulsed Nd:YAG laser operating at 1064 nm with a homogeneous distribution of energy across the beam. Light emitted by the microplasma was detected with an intensified charge-coupled device (iCCD) multichannel detector. The effect of pinhole diameter and the delay time influence on depth analysis have been assessed. An ablation range of only a few nanometers per pulse has been achieved. Depth profiles of various metals (Cr, Ni, Cu) from multilayered samples have been generated by LIBS and depth resolution at different delay times using various pinhole diameters have been calculated and compared.