High-resolution spectrometer for atomic spectrometry

Abstract

Optical spectrometers combining high spectral resolution with multi-pixel detection are used in atomic spectrometry more than ever. Because of their wide spectral range and powerful detection capability, échelle spectrometers coupled with charge-coupled device (CCD) arrays are of increasing interest. We developed a compact échelle monochromator with external order separation for atomic absorption spectrometry with continuum source. Unlike échelle polychromators, in this spectrometer we can exploit the advantages of enlarged dectector height, lower stray light level and less aberrations. In order to limit the spectral bandwidth at the entrance slit of the échelle monochromator, we designed a pre-monochromator whose linear dispersion is controlled by varying the prism angle of a liquid reflection prism. Both the pre-monochromator and the échelle monochromator are arranged in similar Littrow-mountings using off-axis paraboloids with 400 mm focal length. The échelle grating with a blaze angle of 76° yields a spectral bandwidth corresponding to the resolving power of about 140 000 for a 23 µm wide slit.