Relative detection sensitivity in ultrafast spectroscopy: state lifetime and laser pulse duration effects

We present a numerical modelling study employing a kinetic model based on rate equations to investigate the role of excited state lifetime and laser pulse duration on effective relative detection efficiency in time-resolved pump-probe spectroscopy. The work begins to address the critical outstanding problem of photochemical branching ratio determination when excited state population evolves via competing relaxation pathways in molecular systems. Our findings reveal significant differences in detection sensitivity, which can exceed an order of magnitude under typical experimental conditions for excited state lifetimes ranging between 10 fs and 1 ps. We frame our discussion within the widely used approach of ultrafast photoionization for interrogating excited state populations, but our overall treatment may be readily extended to consider a broader range of experimental methodologies and timescales.