Quantitative Elemental Determination in Water by Femtosecond Laser-Induced Breakdown Spectroscopy
Abstract:Examination of the phytoplankton cell photosynthesis system condition and monitoring of concentration of sea water elements that limit phytoplankton cell development require an operative measurement method for determination of chemical elements concentration at the microgram-perliter level. For this purpose, in our research we suggested and developed the method of nanosecond laser spectroscopy, that allowed for measurements of chemical elements in the liquid and phytoplankton cells at the 10-3 – 10-4 g/l level, which ensures its usability for real-time sea water and phytoplankton communities monitoring. However, this method did not allow for the measurements of biogenous elements that limit phytoplankton cell development, and this prompted us to carry out a series of experiments aimed at determination of element concentration at the level of 10-6 g/l.
Research of elemental composition requires preliminary identification of spectral and molecular lines of plasma induced on the surface of sea water and distilled water. This research was carried out with an apparatus described in work.
Spectra of optical breakdown on the surface of water samples under normal atmospheric conditions were obtained for pulse duration – the super-short one, less than 50 fs, and the subpicosecond one of approximately 650 fs. Figure 1 shows the optical breakdown spectrum on the water surface induced with a laser pulse of 50 fs and registered without ICCD gating. This case reveals an intensive continuous spectrum resulting from a super-continuum generation, as well as Bremsstrahlung and recombination radiation. Figure 2 shows an averaging of 20 measurements of optical breakdown spectrum on the sea water surface induced with a laser pulse of 50 fs, registered with a time delay of 20 ns after laser pulse action. Laser pulsing was 10 Hz, exposure time of ICCD camera was 1 μs. This case shows the absence of an intensive continuum. Emission lines of sea water macro-composition are registered. Let us note that all spectrums shown in this paper are not calibrated to the spectral sensitivity of recording equipment.
Document Type: Research Article
Publication date: January 1, 2011