Induced extra-resonances

Y. Prior, A. R. Bogdan, M. Dagenais, and N. Bloembergen. Pressure-induced extra resonances in four-wave mixing. Phys. Rev. Lett., 46 111-114 (1981). 

The principles of this dephasing procedure are discussed in detail elsewhere (/. Magn. Reson. Ser. A 105, 167-183 (1993) ). Here, we note the following features, (a) The optimum dephasing is obtained when the extra offset induced... 

Figure 2 depicts the Induced polarization for a given set of conditions The two side peaks correspond to the Rabi sidebands, and the central feature at lo = 0 is the pressure induced extra resonance at the degenerate frequency. 

The full details of the simulations will be given elsewhere, but in Figure j the results of one such simulation are depicted for conditions similar to those of Figure 2. The similarity between the two cases is obvious, and the figure shows clearly that phase fluctuations can cause extra resonances in the induced polarization. 

The stochastic fluctuation induced extra resonances allow careful investigation of different noise models. It would be Interesting to compare the predictions of various noise models and find out if these extra resonances are useful for distinguishing between different noise processes. Work on this question is in progress. 

On the basis of the experimental data presented above, one cjin exclude on the onset several models for the "blue peak" emission. Firstly, spin-flip collision induced population inversion on the Di transition is not involved - due to both the off-resonant character of the emission and its independence on the buffer gas pressure. Similarly, pressure induced extra resonances are rejected. Stimulated electronic Raman and three photon scattering effects, both by a two or three level system, are dependent on the laser detuning and neither their frequencies are to the blue in the vicinity of the Di line (figure 2) thus, these processes are also excluded. 

As with the quadmpole ion trap, ions with a particular m/z ratio can be selected and stored in tlie FT-ICR cell by the resonant ejection of all other ions. Once isolated, the ions can be stored for variable periods of time (even hours) and allowed to react with neutral reagents that are introduced into the trapping cell. In this maimer, the products of bi-molecular reactions can be monitored and, if done as a fiinction of trapping time, it is possible to derive rate constants for the reactions [47]. Collision-induced dissociation can also be perfomied in the FT-ICR cell by tlie isolation and subsequent excitation of the cyclotron frequency of the ions. The extra translational kinetic energy of the ion packet results in energetic collisions between the ions and background... 

Thirdly, the collision-induced Raman resonances can expand the application of Raman spectroscopy to situations where the conventional Raman susceptibility vanishes. Andrews et al., for example, have demonstrated that sharp vibrational transitions in an initially unpopulated excited electronic state of a molecule can be observed as extra four-wave mixing resonances, even though they cannot be observed in absorption because of rapid dephasing of the electronic transition. In these experiments pentacene molecules were doped in a benzoic acid crystal, and phonon scattering rather than collisions provided the dephasing mechanism. CARS of equally-populated ground state rotational levels in molecules would also become possible by observing collision-induced resonances. 

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