Scaling to millijoule energies for laser-induced breakdown spectroscopy of water samples

摘要

The capabilities of laser-induced breakdown spectroscopy (LIBS) for analysis of water samples with low energy laser pulses was investigated using 355 nm, 10 ns pulses with energies from 3.5 to 100 mJ. In order to optimize the detection limit, the spatial and temporal dependence of the line emission from a sodium solution water jet target in air has been measured, allowing the identification of optimum gating time and observation position for sodium. Careful characterization of the background noise sources in the LIBS detection system has been undertaken, including the continuum emission from the plasma, dark current in the detector array and electron emission noise in the image intensifier. The energy dependence of the limit of detection for sodium in water has been investigated. Single shot detection limits for sodium have been measured ranging from 2 ppm to 200 ppm for laser pulse energies of 100 mJ to 3.5 mJ respectively. For aluminium, the detection limits are over an order of magnitude poorer than for sodium.