Normally polychromators are used with fixed wavelengths. But it is possible to scan each of the fixed polychromator channels over limited ranges of wavelength.
One early way to do this was by rotating
a transparent plate after the entrance slit to form slightly differing
entrance angles onto the grating. The wavelength range that could be
scanned was limited to only about ±0.1 nm before defocussing and other
aberrations became too severe.
A better way, first introduced by Jobin-Yvon Emission (PolyScan®), is to move the entrance slit around the Rowland circle. This limits defocussing and extends the scanning range to about ±2 nm.
Scanning of polychromators is now used routinely for:
- alignment of the primary slit
- verifying the alignment of secondary slits
- checking spectral interferences
- background measurements off peak
- doing multiple lines on one polychromator channel
PolyScan® is a registered trade mark of Horiba Jobin-Yvon, France.
First published on the web: 15 May 2000. Last modified:
20 November, 2007
Author: Richard Payling