The iodine filter in Raman and Brillouin spectroscopy

The absorption spectrum of iodine vapour in the neighbourhood of 5145 AA (Ar+ laser green line) has been examined to determine its usefulness as a filter to reduce parasitic light in Raman and Brillouin scattering experiments. An absorption cell 100 mm in length containing iodine vapour at 50 degrees C attenuates laser light at 5145 AA by a factor of greater than 104. However, other absorption lines occur at -3 and +6 GHz from the laser frequency which limit the useful frequency range of the filter for Brillouin scattering. A large number of narrow, closely spaced absorption lines in the near frequency range (>or approximately=+or-100 AA) cause an irregular but relatively small distortion of Raman line shapes.