, Volume 167, Issue 1, pp 39-45

Polarisation studies on the Raman spectra of cubic crystals

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Polarisation characters of the Raman lines of calcium fluoride (fluorspar) and potassium aluminium sulphate (alum) were investigated under the following conditions. Unpolarised light was incident normally on a face of the crystal making an angle 22.5° with a cubic face and the light scattered transversely along a cubic axis was analysed by a double image prism kept with its principal axes inclined at 45° to the vertical. Under these conditions the depolarisation factors of the Raman lines belonging to the totally symmetric (A), the doubly degenerate (E) and the triply degenerate (F) modes should be respectively =1, >1 and <1. The characteristic Raman line of CaF2 at 322 cm−1 exhibited a depolarisation value less than 1, showing thereby that the corresponding mode is a triply degenerate one (F). The Raman lines observed in the spectrum of K-alum were also classified and the results were compared with those given by previous investigators using standard crystal orientations.

I thank Professor R. S.Krishnan for his valuable help and guidance in the progress of this work. My sincere thanks are also due to Dr. V.Chandrasekharan for the many beneficial discussions I had with him. This investigation was carried out during the tenure of a Junior Research Fellowship awarded to me by the Council of Scientific and Industrial Research.