Correcting distortion in a monochromatic imaging spectrometer for application to elemental imaging by glow discharge-optical emission spectrometry

A method to correct for instrumentally introduced image distortion in a monochromatic imaging spectrometer (MIS) was developed, evaluated and applied to surface elemental imaging in glow discharge-optical emission spectrometry. The method is based on fixed-spatial-frequency images, in which calibration points are localized to characterize the distortion at a given wavelength. In the MIS, a linear increase in image width with wavelength was found in the horizontal dimension, whereas no significant image distortion in the vertical dimension was observed. The ratio between the horizontal and vertical image widths was 18 ± 2% at 400 nm and 46 ± 2% at 750 nm. Correction of distorted images was performed computationally by means of bilinear interpolation. The geometric error, in terms of residuals of the interpolation, was calculated for every pixel in the reconstructed image (512 × 512 array) and typically found to be between 0.12 and 0.18 pixel. The developed method was applied to elemental imaging by glow discharge - optical emission spectrometry as a proof of principle. A glow discharge cell suitable for large-format elemental imaging (7.29 cm-diameter sputtering area) was used for imaging of circular brass samples. Significant differences between vertical and horizontal emission profiles from distorted emission maps (e.g. Zn I 481.05 nm: 30% difference between vertical and horizontal FWHM) could be successfully corrected (4.8% difference after correction) by the method presented here.