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.

Progress in calibration-free laser-induced breakdown spectroscopy

“…Here, the spectrum measured for a single standard sample is used to compensate errors due to the apparatus response function and spectroscopic data. This improvement is however limited, as the spectroscopic data -that are transition probabilities and Stark broadening parameters -impact the amount of self-absorption [57], whereas the apparatus response has a linear influence on the measured line intensity [58]. Consequently, the accuracy improvement due to the single calibration step works properly only when optically thin lines are used, or when the elemental fractions to be measured are close to those of the standard sample.…”

“…(Adapted from Ref. [58]) ical measurements when it is performed in appropriate experimental conditions [28,29,30], there are still obstacles that hinder its use in industrial applications.…”

“…Echelle spectrometers exploit dispersion of light into two orthogonal directions, and both their spectral and intensity calibration are therefore sensitive to temperature variation [73]. Thus, a method for rapid checking and correcting the apparatus response R app (λ) was proposed [58].…”

“…Echelle spectrometers are extremely sensitive to temperature variation and even small changes of the order of 1 K may alter the spectral calibration and the apparatus response function [73]. The loss of calibration may even occur when the spectroscopic apparatus is located in a temperature-stabilized laboratory environment, because the heat generated by the detector may cause temperature variation of the optical system [58]. Calibrationfree LIBS measurements should therefore be performed with T -stabilized echelle spectrometers to ensure highest accuracy.…”

On the Omnipresence and Potential of Plasma Technology

“…Even though conventional plasma-based fluorescent lamps have been available since the 1930s, plasmas still feature a high potential in lightening technology. Here, novel radiation sources with unique properties, such as, for example, extremely short wavelengths [3] for lithography purposes or highest homogeneity [4], well suited for calibration processes [5], were introduced recently. Moreover, the potential of plasmas as functional devices for the generation of short light pulses in modern Q-switched laser sources was reported [6].…”