Characterization of aerosols produced by laser-matter interaction
Congress title :1st workshop on the "Dust in Fusion Plasmas"
Congress location :Warsaw
Congress date :08/07/2007
A surface decontamination process is here considered: laser ablation. The aim of this paper is to present the different techniques to perform a physical characterization of aerosols produced during the process. Two examples will be discussed: one is concerning paint stripping and the other one deals with graphite tiles ablation coming from Tokamak.
The physical characterization is mainly focused on the number, the size distribution and the morphology of particles produced during laser ablation. The particle number was measured with a Condensation Particle Counter (CPC) and their size distribution with an Engine Exhaust Particle Sizer (EEPS, working range: 5.6-560 nm) and an Aerosizer (working range: 0.5-100 µm). In addition, a filtration system is used in order to collect the particles for Transmission Electronic Microscopy (TEM) analyses.
For acrylic paint stripping, the experiments were carried out using a Nd:YAG laser working at 532 nm, the pulse duration was 5 ns. The repetition rate and the fluence have been varied respectively from 0.1 to 10 Hz and from 0.2 to 11 J.cm-2. The results showed that the aerosol produced during a laser shot is both composed of nanoparticles and submicronic particles. A mode around 70 nm was detected by the EEPS and another one around 717 nm by the Aerosizer. Moreover, the TEM analyses allow us to suppose that the nanoparticles would be aggregates of primary particles. The submicronic particles would be large spherical particles.
For graphite tiles ablation, the experiments were carried out using an IPG laser (model YLP-1/120/20) working at 1 µm, the pulse duration was 100 ns. The energy of each pulse was fixed at 1 mJ and the repetition rate at 20 kHz. Two graphite tiles with hydrocarbon co-deposited layer on one side were studied. We studied both the front face of the tile (side co-deposited layer) and the back face of the tile (side substrate). A mode around 10 nm was detected by the EEPS for the side substrate. The mode for the side layer was located towards 60-90 nm. A second mode around 700-800 nm was observed by the Aerosizer for all the tiles at the same time on the side layer and on the side substrate.
The further work will be to perform complementary chemical analyses on particles and gases and to set up in-situ optical methods to follow the stages of formation of the particles.