Raman Spectroscopy with Sub-Natural Linewidth

A very interesting method for achieving sub-natural linewidths of optical transitions is based on induced resonant Raman spectroscopy which may be regarded as a special case of optical-optical double resonance (Sect. 10.4). The pump laser LI is kept on the molecular transition l) 2) (Fig. 14.49) 

When both laser waves with the wave vectors kp and kg are sent colli- 

Integration over the velocity distribution N(Vg) of the absorbing mole- 

Of course, one cannot get accurate information on the level width 73 from (14.61) unless all other contributions to 7g are sufficiently well 

The small-signal width of the OODR signal 7g becomes essential if the levels [3) are high-lying rotation-vibration levels of heavy molecules closely below the dissociation limit where the level density may become very high. 

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