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We report the quantitative elemental analysis of a steel sample using calibration-free laser-induced breakdown spectroscopy (CF-LIBS). A Q-switched Nd:YAG laser (532 nm wavelength) is used to produce a plasma by focusing it onto a steel sample in air at atmospheric pressure. The time-resolved spectra from atomic and ionic emission lines of the steel elements are recorded by an echelle grating spectrograph coupled with a gated intensified CCD camera and are used for the plasma characterization and quantitative analysis of the sample. The time delay at which the plasma is in local thermodynamic equilibrium as well as optically thin, necessary for elemental analysis, is deduced. An algorithm for the CF-LIBS relating the experimentally measured spectral intensity values with the basic physics of the plasma is developed and used for the determination of Fe, Cr, Ni, Mg, and Si concentrations in the steel sample. The analytical results obtained from the CF-LIBS technique agree well with the certified values of the elements in the sample, with relative uncertainties of less than 5%.

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Laser-induced steel plasma is generated by focusing a Q-switched Nd:YAG visible laser (532 nm wavelength) with an irradiance of ∼ 1 × 10 9 W/cm 2 on a steel sample in air at atmospheric pressure. An Echelle spectrograph coupled with a gateable intensified charge-coupled detector is used to record the plasma emissions. Using time-resolved spectroscopic measurements of the plasma emissions, the temperature and electron number density of the steel plasma are determined for many times of the detector delay. The validity of the assumption by the spectroscopic methods that the laser-induced plasma (LIP) is optically thin and is also in local thermodynamic equilibrium (LTE) has been evaluated for many delay times. From the temporal evolution of the intensity ratio of two Fe I lines and matching it with its theoretical value, the delay times where the plasma is optically thin and is also in LTE are found to be 800 ns, 900 ns and 1000 ns.