Raman spectrum of rock-salt under high resolution

The original investigation of Rasetti as well as my later work on the Raman effect in rock-salt were carried out using a Hilger medium-size quartz spectrograph for recording the faint second-order spectrum. In view of the fundamental importance of the case, it appeared desirable to re-investigate the subject, using the largest possible resolution and dispersion. Various improvements in experimental technique, including especially the efficient filtering of the exciting radiation before its entry into the spectrograph, steady running conditions of the arc and the temperature control of the spectrograph, have enabled me to work with the larger Hilger E1 quartz spectrograph for recording the Raman spectrum. Using a fine slit which necessitated an exposure of 160 hours, a record was obtained in which the details are not sensibly obscured by halation and which exhibits the true nature of the spectrum unambiguously