High Energy Double Peak Pulse Laser Induced Plasma Spectroscopy for Metal Characterization Using a Passively Q-Switched Laser Source and CCD Detector.

Here, the development and testing of a portable double peak pulse laser induced plasma spectroscopy (DPP-LIPS) based on passively Q-switched Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) laser excitation is reported. The latter delivered structured laser pulses at a repetition rate of up to 20 Hz, including two energy peaks of about 100 mJ each with a relative temporal spacing of about 80 µs. Plasma spectra were collected using a low-cost Czerny-Turner spectrometer equipped with a non-intensified CCD (Charge-Coupled Device) array. Such a DPP-LIPS setup is technologically simpler and cheaper than the usual ones. Despite the relatively large temporal separation between the mentioned laser peaks, significant spectral intensity enhancements with respect to the usual single peak pulse configuration were observed. The amplification factor measured ranged between 2 and 10, depending on the specific emission peaks and the Q-switched configuration, and a consequent significant improvement of the detection limit of trace elements was observed. The instrument was calibrated for the quantitative analysis of copper alloy through systematic measurements carried out on reference samples and was then tested in an example archaeometric characterization of a statuette from the Egyptian Museum of Florence.