Stimulated level crossing

So far we have considered level crossing monitored through spontaneous emission. A level-crossing resonance can also manifest itself as a change in absorption of an intense monochromatic wave tuned to the molecular transition when the absorbing levels cross under the influence of external fields. The physical origin of this stimulated level-crossing spectroscopy is based on saturation effects and may be illustrated by a simple example [845]. 

Fig. 7.7 Stimulated level-crossing spectroscopy with a common lower level (a) level scheme and (b) saturation holes in the Doppler-broadened population distribution with and without magnetic field...

M.S. Feld, A. Sanchez, A. Javan, Theory of stimulated level crossing, in IntT Colloq. on Doppler-Free Spectroscopic Methods for Single Molecular Systems, ed. by J.C. Lehmann, J.C. Pebay-Peyroula. (Ed. du Centre National Res. Scient., Paris, 1974), p. 87... 

J.S. Levine, P. Boncyk, A. Javan, Observation of hyperfine level crossing in stimulated... 

It is well established that in response to a variety of agents that cause an increase in intracellular calcium levels and stimulate LT synthesis, including calcium ionophore, cross-linked IgE receptors, thapsigargin and f-MetLeuPhe, 5-LOX translocates from a soluble to a membrane fraction in cells [26,27,39-41]. By subcellular fractionation and immunoblot analysis, compounds which bind to FLAP both inhibit and reverse this membrane association in a concentration-dependent manner [42—45]. For structural analogues of MK-886 and six different series of quinoline compounds, there is a correlation between inhibition of 5-LOX translocation and cellular LT synthesis [43,46-48], suggesting that FLAP regulates the membrane association of 5-LOX. 

A number of stimulated level-crossing experiments have been performed on the active medium of gas lasers where the gain of the laser transition is changed when sublevels of the upper or lower laser level cross each other. 

The whole gain tube is for instance placed in a longitudinal magnetic field and the laser output is observed as a function of the magnetic field. One example is the observation of stimulated hyperfine level crossings in a Xe laser [10.96], where accurate hyperfine splittings could be determined. 

Although saturation effects may influence the line shape of the level-crossing signal, for small saturation it may still be essentially Lorentzian. Stimulated level-crossing spectroscopy has been used to measure Lande factors of atomic laser levels with high precision. One example is the determination of gi P ) = 1.3005 0.1% in neon by HERMANN et al. [10.97]. 

---