Echelle spectrometer calibration by means of laser plasma

Abstract

Echelle spectrometers enable the observation of large spectral windows with high resolving power in single recordings. However, these devices are strongly sensitive to temperature variations and even small changes may tamper both the wavelength and the intensity calibration. Here we propose a method for rapid checking and rectifying the calibration using the emission of a plasma produced by pulsed laser ablation of steel. A spectrum recorded with a large delay between the laser pulse and the observation gate exhibits sharp lines that are exploited for wavelength calibration. A second spectrum is recorded with a shorter delay, when the plasma properties enable the accurate simulation of the plasma emission spectrum. The apparatus response is deduced from the ratio of measured over computed line intensities. The method is of particular interest for laser-induced breakdown experiments in which the calibration measurements are performed via the simple change of the irradiated sample.