IMPROVEMENTS IN SPECTRAL-LINE SHAPE REPRODUCTION FROM SPECTROGRAPHS WITH CCD DETECTION

A new procedure has been developed which improves the reproduction of spectral line shapes from spectrographs with charge-coupled device (CC D) detection. The procedure, which requires that the image of the entr ance 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 spe ctrum. 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 v ariation 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 emiss ion spectroscopy (ICP-AES).