Two-photon absorption resonance enhancement

Benzene ions are produced in an effusive molecular beam inside the acceleration field of a reflectron time-of-flight mass spectrometer /12/. (see Fig. 3). Laser 1 is tuned to the frequency of the 6 i or 60116 -1 band and produces, via a resonance-enhanced two photon absorption, state- and energy-selected benzene cations. 

Figure 8 Multiphoton excitation and ion spectroscopy Bottom spectrum cold, mass selected UVspectmm (S, <- So transition) of fluorobenzene, providing wavelengths for efficient and selective ionization. Middle spectra photoelectron spectra induced by UV-resonance enhanced two-photon absorption. Choosing different intermediate states [S,(0,0) or S,(6b )] results in different populations of the final fluorobenzene radical cations. Top spectrum spectroscopy of the excited ionic state of the fluorobenzene radical cation measured by muKiphoton dissociation spectroscopy. The ions have been prepared via the neutral 0°o transition. A special excitation scheme has been used to optimize cation spectroscopy (for further details see text).

In this work we will describe the next generation of first-order Doppler-free saturated absorption experiments, carried out in a three-level system ° in fgst atom/ion beams as well as resonant stimulated Raman processesand resonantly enhanced two-photon absorption, in all three cases taking full advantage of the velocity... 

In the cascade configuration shown in Fig.4, coherent processes dominate. On exact resonance, again given by Eqs.(2) and (3), a resonantly enhanced two-photon absorption n- takes place. This absorption is Doppler free to first order and is, because of its coherent nature, not dependent on the first-order broadening due to the transverse velocity distribution. Thus a resolution, only limited by the homogeneous linewidth Y is easily obtained. 

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