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Optical micro-lens array for laser plasma generation in spectrochemical analysis

: Sturm, V.


Journal of analytical atomic spectrometry 22 (2007), Nr.12, S.1495-1500
ISSN: 0267-9477
Fraunhofer ILT ()

A Q- switched Nd: YAG laser beam is focused by an optical micro- lens array to produce a laser plasma at a target. The spatial intensity distribution in the focal plane is an array of closely-spaced high intensity spots. At a laser output energy of similar to 200 mJ ( wavelength 1064 nm, pulse duration similar to 8 ns, repetition rate 10 Hz), a laser- induced air breakdown is observed in similar to 47 spots inside an area of similar to 9 mm diameter at the focal plane. For solid targets, a laser plasma is produced with a micro- lens array for spectrochemical analysis, e. g., laser- induced breakdown spectroscopy. Emission spectra of the laser plasma plume as well as pulse- to- pulse measurements with a simultaneous spectrometer are taken from a rotating slag sample with inhomogeneous distribution of species such as SiO2 or CaO. For the micro- lens configuration, the variation of the spectral line emission, e. g., of Si and Ca lines, is reduced in comparison with a single lens focusing showing the averaging effect of the micro- lens array produced plasma. A more representative analysis of the average concentration of inhomogeneous samples can be expected without elaborate and time- consuming sequential scanning of extended sample areas. Calibration curves for SiO2 and Fe2O3 are taken with samples of silicate glasses.