Testing of an Echelle Spectrometer as a LIBS Detector at Sandia

Some useful information has been obtained regarding the potential use of the echelle spectrometer system for Laser-Induced Breakdown Spectroscopy (LIBS) monitoring applications, despite the AOTF-computer operational problems during the Sandia site-test. Currently, the use of the echelle spectrometer with the LIBS system is not suitable for trace-level analyte detection. This is due, in part, to the lower light throughput of the echelle spectrometer system compared to the SpectraPro-275. The low duty cycle of the LIBS system, which results from the use of a low-repetition-rate (but low-cost and portable) laser, also limits the detection sensitivity achievable using a high-resolution spectrometer. At high analyte concentrations, the echelle spectrometer is able to resolve spectral interferences including the Cd-As line pair at 228.8-nm and other LIBS emission features not resolved using the SpectraPro-275. A definite positive result obtained is the determination that at the high resolution of the echelle spectrometer, time-gating of the CCD detector is not necessary to discriminate analyte spectral signals from the LIBS background emission. The cost of the gated CCD and associated electronics is a significant portion of the cost of the Sandia LIBS system. Incorporation of a low-cost version of the echelle spectrometer for process monitoring applications not requiring trace-level detection could make LIBS a more viable technique where cost is a limiting factor. We hope to have the opportunity to perform additional collaborative work using the AOTF-echelle spectrometer for on-line LIBS monitoring applications, in order to demonstrate the advantage of rapid line-switching (using the AOTF) and simultaneous detection of multiple emission features across the spectral range of the echelle