ROA Instrumentation

    The two current Glasgow ROA instruments are based on a backscattering geometry, which  is essential for the routine measurement of ROA spectra of biomolecules in aqueous solution. An incident visible argon ion laser beam is focused into the sample, which is held in a small rectangular cell. The cone of backscattered light is collected by means of a 45° mirror with a small central hole to allow passage of the incident laser beam. This backscattering ROA collection system, including the crucial Lyot depolarizer, is based on one designed and implemented by Werner Hug in the late 1970s. The Raman light is thereby reflected into the collection optics of a single-grating spectrograph (Kaiser Holospec). The charged-coupled device (CCD) camera used as a multichannel detector permits measurement of the full spectral range in a single acquisition. To measure the tiny ROA signals, the spectral acquisition is synchronized with an electro-optic modulator (EOM) used to switch the polarization of the incident laser beam between right and left circular at a suitable rate. Further details may be found in:

Raman optical activity instrument for studies of biopolymer structure and dynamics. L. Hecht, L. D. Barron, E. W. Blanch, A. F. Bell and L. A. Day (1999). J. Raman Spectrosc. 30, 815-825.

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