A Method for Direct Scanning of the Purely Isotropic Part of Raman Scattered Light

In a recent paper Kiefer and Topp have shown how the depolarization ratio can be scanned automatically as a function of Raman shift. By means of a rotating split polarization rotator which is positioned in the laser beam and of a gated, two-channel computing photon counting system the quantities I⊥, I∥, and ρ = I⊥/I∥ can be directly and simultaneously recorded. By combining this technique with the method of difference Raman spectroscopy one is also able to subtract the anisotropically scattered light (I⊥, ~ 3γ) from the I∥ spectrum which contains isotropically as well as anisotropically scattered Raman light (I∥ ~ 45α−2 + 4γ2). Although this technique was already suggested in Ref. 1, the present note shows (to our knowledge) the first example of a real time scan of the purely isotropic part of Raman scattered light (trace scattering).