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Applied Physics B

Large-scale collisional energy transfer in laser-pumped metastable Ca atoms: Excitation of resonance states of Ca II

Muhammad Arshad Khan, M.A. Gondal, M. H. Rais

Published Oct 1, 1995• 3 citations
Publisher
DOI
10.1007/bf01081540

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Role of some selected intermediate states of Ca I in the collisional excitation of 4p2P states of Ca II in a laser-pumped Ca vapour

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The role of some intermediate states, e.g. 4s5p 3 P, 3d4p( 1 D, 3 F) of Ca I in the collisional excitation of the 4p 2 P 3/2,1/2 states of Ca II (located at 74720.35 and 74497.46 cm -1 above the ground state of Ca I) following pulsed-laser pumping of the 4s4p 3 P 1 state of Ca I (E ex =15210.063 cm -1 ), is investigated. A 'pump' and 'probe' technique is employed together with the study of fluorescent emission. The 'probe' laser selectively prepares a substantially higher population of a specific intermediate state in Ca I and the increase in the fluorescent intensity of the 4p 2 P 3/2 - 4s 2 S 1/2 transition of Ca II is read as the relative strength of the particular collision channel utilizing that intermediate state. It is found that the 3d4p 1 D 2 state has the strongest influence.

Journal of Physics B Atomic Molecular and Optical Physics•Mar 14, 1995•2 citations
Experimental results are reported where the rates of collisional energy transfer in optically prepared atomic metastable states are considerable compared with the rate of normal radiative decay. A remarkable consequence is a large increase in the effective lifetime of some excited states lying above the optically prepared state. The specific case of calcium is presented here as an example where over a 1000-fold increase in the lifetime of 4s3d 3 D states has been experimentally measured following pulsed-laser pumping of 4s4p 3 P 1 metastable state. This can have important applications in the development of quasi-CW lasers. The possibility of populating 4s4p 1 P 1 and 4s5s 3 S 1 states through energy pooling collisions is also investigated. The rate coefficient for pooling to the 4s5s 3 S 1 state is estimated to be 10 -8 -10 -9 cm 3 s -1 .
Abstract : This report describes work addressing the problems of collisional induced oscillator strength and energy transfer from metastable states in Group IIA alkaline earth metal atoms. The quenching of CA 3PJ states when perturbed by rare was atom collisions is investigated and such quenching is found to be negligable. The CA 1D2 state, however shows considerable collisional induced effects. Calculations have been performed which show that collision cross-sections for transfer of electronic excitation may be switched from the low values typically associated with off-resonant processes to the high values associated with resonant processes by using a strong laser to bring dressed states in one atom in and out of resonance with bare states in another atom. Keywords: Slow atomic collisions; Chemical lasers.
The role of some intermediate states, e.g. 4s5p 3 P, 3d4p( 1 D, 3 F) of Ca I in the collisional excitation of the 4p 2 P 3/2,1/2 states of Ca II (located at 74720.35 and 74497.46 cm -1 above the ground state of Ca I) following pulsed-laser pumping of the 4s4p 3 P 1 state of Ca I (E ex =15210.063 cm -1 ), is investigated. A 'pump' and 'probe' technique is employed together with the study of fluorescent emission. The 'probe' laser selectively prepares a substantially higher population of a specific intermediate state in Ca I and the increase in the fluorescent intensity of the 4p 2 P 3/2 - 4s 2 S 1/2 transition of Ca II is read as the relative strength of the particular collision channel utilizing that intermediate state. It is found that the 3d4p 1 D 2 state has the strongest influence.