Experimental and theoretical study of the imprisonment of the Kr S-1(0)-P-3(1) 123.58 nm resonance radiation

The apparent decay of the Kr P-3(1) level, populated by means of a 3-photon excitation process, is studied in the [0.006, 10] Torr pressure range for two different geometry's of the imprisonment cell. The reproducibility of t he experimentally obtained fundamental mode radiative decay rates beta is b etter than 3%. For the theoretical description of the imprisonment process effects of partial frequency redistribution must be accounted for. It is fo und that the analytical expression of Post for the fundamental mode radiati ve decay rate underestimates beta in the pressure region around 0.03 Torr, due to the Jefferies-White approximation, which is used in this formula. De cay rates, deduced from Monte Carlo simulations of the imprisonment process , in which no approximations of the partial frequency redistribution functi ons are made, show excellent agreement with the experimental results for pr essures p < 0.6 Torr. A natural lifetime tau(n) = 3.5 ns is obtained for th e P-3(1), resonance state in Kr. The value of the FWHM of the pressure broa dened line profile in the impact approximation is derived and compared with previous results in literature. For p greater than or equal to 0.6 Torr th e present theory, based on the impact approximation, predicts a nearly cons tant beta. The good accuracy of our results allows us to observe a distinct decrease of beta with increasing pressure in the [0.6, 4] Torr range. In t he corresponding optical depth range the impact approximation is invalid an d the duration of collision effects has to be taken into account. A general ised form of the formula of Post, valid regardless the duration of the coll isions, is proposed. This formula yields an accurate description of the obs erved decrease of the decay rate beta. (C) 2000 Elsevier Science Ltd. All r ights reserved.