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Journal of Physics B Atomic and Molecular Physics

Production of large numbers of atoms in a selected excited state by laser optical pumping: calcium

Thomas J. Mcilrath, John L. Carlsten

Published Apr 1, 1973• 45 citations
Publisher

Abstract

An experiment is described in which large numbers ( approximately 10 16 ) of calcium atoms are placed in the 4s4p 3 P metastable level by optical pumping with a tunable dye laser and then studied spectroscopically. Equations governing the degree of excitation by the laser are derived. Predictions of the theory are shown to be in good agreement with experimental results. In particular, at low optical depths produced by 10 15 ground state atoms cm -2 the dye laser raises approximately 50% of the calcium atoms into the metastable state. At higher optical depths associated with 10 17 ground state atoms cm -2 the number of excited states is limited only by the laser energy and line width. For the dye laser used the largest number of metastables produced was approximately 10 16 . The absorption spectra of the 4s4p 2 P level is seen out to 4s4p 3 P to 4s22d 3 D. The relaxation rate between the excited state fine structure is studied directly with an optically delayed dye laser continuum. Other applications of this technique of producing large numbers of excited states are briefly discussed.

DOI
10.1088/0022-3700/6/4/023

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Stark mixing of high-lying calcium levels by laser-produced charges

S A Borgström, Jan R. Rubbmark

Using a pulsed tunable dye laser pumped by a nitrogen laser, the 4s4p 1 P 1 0 level in Ca I was selectively populated from the 4s 2 1 S 0 ground state. Transitions from the 4s4p 1 P 1 0 level to 4sns 1 S 0 and 4snd 1 D 2 and, for n approximately=20, also to 4snp 1 P 1 0 and 4snf 1 F 3 0 were observed. The latter transitions arise because of Stark mixing of Rydberg states in the field of laser-produced ions and electrons. By applying a voltage to electrodes in the calcium vapour, Stark shifts were measured for levels belonging to the 4snf 1 F 3 0 and 4s(n+1)d 1 D 2 series in a region where the series cross. Diagonalisation of the energy matrix for interacting states with hydrogenic dipole matrix elements gave theoretical Stark shifts in reasonable agreement with those measured. The 4snf 1 F 3 0 series has been extended from n=12 to n=28 by absorption from 4s3d 1 D 2 . The latter level was found to be populated by stimulated emission from 4s4p 1 P 1 0 .

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Collisional recycling of excited atomic populations in Ca in a thermionic diode following pulsed-laser excitation of a metastable state

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

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 .

Journal of Physics B Atomic Molecular and Optical Physics•Jul 28, 1994•12 citations
An experiment is described in which large numbers ( approximately 10 16 ) of calcium atoms are placed in the 4s4p 3 P metastable level by optical pumping with a tunable dye laser and then studied spectroscopically. Equations governing the degree of excitation by the laser are derived. Predictions of the theory are shown to be in good agreement with experimental results. In particular, at low optical depths produced by 10 15 ground state atoms cm -2 the dye laser raises approximately 50% of the calcium atoms into the metastable state. At higher optical depths associated with 10 17 ground state atoms cm -2 the number of excited states is limited only by the laser energy and line width. For the dye laser used the largest number of metastables produced was approximately 10 16 . The absorption spectra of the 4s4p 2 P level is seen out to 4s4p 3 P to 4s22d 3 D. The relaxation rate between the excited state fine structure is studied directly with an optically delayed dye laser continuum. Other applications of this technique of producing large numbers of excited states are briefly discussed.
A simple theory describing selective excitation of a three-level atom with a tuneable laser is developed. Effects of number density, line widths and laser parameters on the final populations of the levels with laser excitation are discussed. An experiment is described in which a tuneable dye laser is used to pump large numbers of barium atoms into the 6s5d 3 D metastable term from the (bs) 2 1 S 0 ground state via the 6s6p 3 P term. The theory for the interaction of the laser with this 'three-level system' predicts that approximately 80% of the barium atoms should be excited into the 3 D term. Experimentally the largest amount of excitation to the 3 D term observed was (78+or-5)%.
The ionization of calcium atoms resonantly excited to the 4s4p 3 P 1 metastable state is investigated. In particular, the influence of various experimental parameters on the total ionization yield and the rate of its growth are reported. Maximum ionization yield was obtained with the buffer gas (Ar) pressure in the range 100-650 mbar. Furthermore, the time history of depopulation of the metastable state 4s4p 3 P 1 monitored in a 'pump' and 'probe' experiment using a second dye laser tuned to the 4s4p 3 P 1 -4s5s 3 S 1 transition is presented. The effective lifetime of the 4s4p 3 P 1 state is shortened to 31+or-2 mu s at 850 degrees C and 800 mbar Ar pressure from the known value of about 350 mu s.
Using a pulsed tunable dye laser pumped by a nitrogen laser, the 4s4p 1 P 1 0 level in Ca I was selectively populated from the 4s 2 1 S 0 ground state. Transitions from the 4s4p 1 P 1 0 level to 4sns 1 S 0 and 4snd 1 D 2 and, for n approximately=20, also to 4snp 1 P 1 0 and 4snf 1 F 3 0 were observed. The latter transitions arise because of Stark mixing of Rydberg states in the field of laser-produced ions and electrons. By applying a voltage to electrodes in the calcium vapour, Stark shifts were measured for levels belonging to the 4snf 1 F 3 0 and 4s(n+1)d 1 D 2 series in a region where the series cross. Diagonalisation of the energy matrix for interacting states with hydrogenic dipole matrix elements gave theoretical Stark shifts in reasonable agreement with those measured. The 4snf 1 F 3 0 series has been extended from n=12 to n=28 by absorption from 4s3d 1 D 2 . The latter level was found to be populated by stimulated emission from 4s4p 1 P 1 0 .
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 .