Monitoring of light-element concentration in steel is very important for quality assurance in the steel industry. In this work, detection in open air of trace phosphorus (P) in steel using laser-induced breakdown spectroscopy (LIBS) combined with laser-induced fluorescence (LIF) has been investigated. An optical parametric oscillator wavelength-tunable laser was used to resonantly excite the P atoms within plasma plumes generated by a Q-switched Nd:YAG laser. A set of steel samples with P concentrations from 3.9 to 720 parts in 10(6) (ppm) were analyzed using LIBS-LIF at wavelengths of 253.40 and 253.56 nm for resonant excitation of P atoms and fluorescence lines at wavelengths of 213.55 and 213.62 nm. The calibration curves were measured to determine the limit of detection for P in steel, which is estimated to be around 0.7 ppm. The results demonstrate the potential of LIBS-LIF to meet the requirements for on-line analyses in open air in the steel industry.
The efficient second-Stokes generation at 1120 nm is obtained from a KTiOAsO4 (KTA) crystal. The relative Raman scattering cross sections of KTA with respect to YVO4 are determined by studying their spontaneous Raman scattering spectra at room temperature. A 30-mm-long KTA crystal is placed inside the cavity of a diode-end-pumped acousto-optically Q-switched Nd:YAG laser. With a pump power of 6.7 W and a pulse repetition rate of 20 kHz, the second-Stokes (1120 nm) power of 0.63 W is obtained, corresponding to a diode-to-second-Stokes conversion efficiency of 9.4%.
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