Improvements in Spectral Line Shape Reproduction from Spectrographs with CCD Detection

Abstract

A new procedure has been developed which improves the reproduction of spectral line shapes from spectrographs with charge-coupled device (CCD) detection. The procedure, which requires that the image of the entrance aperture be slanted with respect to the columns of the CCD pixels, increases the effective spatial resolution of the instrument without the necessity for mechanical scanning of the exit focal plane and the acquisition of multiple images. A simple algorithm is described which converts the recorded two-dimensional data into a one-dimensional spectrum. The resultant spectrum lacks the stepped and angular appearance normally associated with CCD-derived spectral data. In addition, the dependence of the peak height signal with the peak center position for narrow spectral features is substantially reduced. For example, the variation in peak height signal with the intra-pixel peak position, for a spectral line with full width at half-maximum of 2.0 pixels, can be reduced from 15% to only 3%. The procedure has been implemented on an Echelle spectrograph used for inductively coupled plasma atomic emission spectroscopy (ICP-AES).