Automatic wavelength calibration procedure for use with an optical spectrometer and array detector

Abstract

Échelle spectrometers with cross-dispersion are often used in emission spectroscopy owing to their high spectral resolution and good light throughput. The resultant two-dimensional dispersion plane is ideally suited to array detectors such as the charge-injection device (CID) or charge-coupled device (CCD). The successful coupling of an échelle spectrometer with an array detector permits true simultaneous spectroscopy to be performed over a large spectral range. In order to correctly identify spectral features it is necessary to have an accurate wavelength calibration function which maps the CCD/CID pixel co-ordinates to wavelength. A new approach to the wavelength calibration of optical spectrometers with array detection is proposed that does not involve a direct modelling of the spectrometer dispersion. Instead, the difference between an ideal conceptual spectrometer and the physical instrument is modelled. The procedure is able to compensate for the effects of manufacturing tolerances and local temperature and pressure conditions. Preliminary results, obtained by simulation with a computer-modelled échelle spectrometer, has shown that a sub-pixel accuracy in the predicted position of spectral lines can be achieved over a temperature range 5–35 °C.