Abstract
Within the framework of a three-level model, the process of three-photon ionization with one-photon resonance between two excited levels (with the lower one being initially unpopulated) is considered using the density matrix method. It is shown that such resonance can result in the appearance of a maximum in the three-photon ionization spectrum when detuning between the resonance wavenumber and the wavenumber of the transition responsible for the lower excited level being populated exceeds the laser radiation linewidth by more than three orders of magnitude.
Highlights
Interest in the study of multiphoton ionization has remained consistently high for more than half a century [1,2,3,4,5,6]
The value γL = 0.2 cm−1 was chosen from the consideration that at such a value, in our opinion, the influence of the Lorentzian “wings” of the laser radiation spectrum on the probabilities of the transitions under study, first of all that of the non-resonant population of the 6s6p 1 P o1 level, can be neglected
It is shown that such resonance can result in the maximum appearance in the three-photon ionization spectrum due to the non-resonant population of the lower excited level 2 with a detuning
Summary
Interest in the study of multiphoton ionization has remained consistently high for more than half a century [1,2,3,4,5,6]. At the wavenumber ω = 18,140 cm−1 was 80 cm−1 which was more than an order of magnitude larger than the laser radiation linewidth (∆ω ≈ 2–3 cm−1 ) This indicates a substantially non-resonant character of the lower excited 6s6p 1 P o1 level (level 2) population. The concentration of the studied atoms (in a beam or vapor) did not exceed 1012 cm−3 This allows one to exclude the processes of collisions and multiphoton scattering from the possible mechanisms of population of the lower excited level 2, in this case 6s6p 1 P o1. Practically the only mechanism that makes it possible to explain the resonant transitions of type (3) is non-resonant population of the lower excited level 2 in the field of pulsed laser radiation [14]. There are no quantitative calculations in the literature that confirm and describe this process
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