Population rate equations modelling of a resonant ionisation process

Abstract

A four level population rate equations model is described and is used to interpret published resonant ionisation data for the Yb atom. Three different laser wavelengths were used in the experiment for the excitation steps. The ion-yield graphs a s a function of laser fluences are well reproduced. From the analysis, the Einstein coefficient for the transition of the 17 3P2 state to the 7 3S1 state is determined to be 9940 s-1 with an uncertainty of 10%. The sensitivity of multi-photon processes to a time structure in the laser pulse is studied and important differences in ion yield are calculated for excitation steps involving simultaneous absorption of two or more photons.

Nanosecond Versus, Picosecond Molecular Multiphoton Fragmentation of Keteneand Cyclohexane

“…In the alternative pathway, involving the participation of an intermediate, dissociation from the two-photon excited molecular Rydberg state could compete favourably with up-pumping giving rise to a species that dissociates after the absorption of a third photon. To clarify this point a simple rate equation model has been employed to account for the variation of CH(A) intensity with the duration of the laser pulse [10]. 10-20 cm2, and of the dissociative lifetime of the corresponding one and two-photon molecular excited states, tl--30ps and t2 ps,…”

“…Therefore, it should be reasonable to assume that the ionization signal measured with 10ps laser pulses is due mainly to molecular parent ions. The photoionization processes taking place at the two studied wavelengths in the picosecond domain were treated by using a three level population rate equation model [10]. A proper description of the procedure and its extension to the nanosecond domain will be published shortly.…”

“…Multiphoton dissociation of ketene at 290.5nm was studied after irradiation of the first excited singlet state with laser pulses of 4 ns and 10ps pulsewidths. Analysis of the photofragment fluorescence spectra in the two time domains with the help of a rate equation model [10] sheds light on the mechanisms that are responsible for the production of the observed photofragments. Cyclohexane is one of the few reported examples of a molecule with a giant resonance [11].…”

“…Ionization signal as a function of the pressure of cyclohexane induced by 290.5 nm laser pulse focused with different focal length lenses. Data taken with pulses of: a)10 ps, open symbols, b) 4 ns, solid symbols.…”