The phenomenon of resonance Raman scattering was predicted by Placzek in 1934. From that time to the time of the invention of the laser in 1960, resonance Raman work was mostly performed with a large Hg arc source and with a relatively large sample volume. After the laser was introduced to Raman spectroscopy in 1962, it became the primary source for Raman spectroscopy. For far-UV resonance Raman spectra, the signals are selectively enhanced 10<sup>2</sup> to 10<sup>6</sup> times for vibrations which are associated with electronic transitions. Fluorescence or phosphoresence background from the impurity or sample itself is reduced either by the low quantum yield in the far-UV region or by the fast internal conversion to the lowest energy singlet or triplet excited state.
C. Chen, B. W. Smith, J. D. Winefordner, and M. J. Pelletier, "Near-Ultraviolet Resonance Raman Spectroscopy Using Incoherent Excitation," Appl. Spectrosc. 48, 894-896 (1994)