Coherence and Quantum Optics V pp 1063-1072 | Cite as

# Turning off Decay: Population Trapping in Bound-Continuum Excitation

## Abstract

A discrete state which is coupled to a continuum of states usually finds its time-development damped by an irreversible loss of a Markovian or near-Markovian kind. The decay is described by a close-coupling, of which the Weisskopf-Wigner model is the best known, and laser-induced photcionisation and autoionisation more recently-studied examples. Attention has recently focussed on the exploitation of atomic coherence effects to disengage such decay channels by the creation of superposition states stable against photoionisation or decay.^{1} Such superposition states are modelled as dressed states of the atom-field system^{2} whose decay rates can be reduced to zero by a combination of width-subtracting linenarrowing^{3} and off-diagonal damping.^{4} Such effects have been studied in Raman excitation,^{5} quantum beat fluorescence,^{6} laser-excited autoionisation,^{7} predissociation^{8} and induced continuum structure.^{2} We review the theory of such effects and discuss their importance in multiphoton excitation. Two examples will be described in detail. First, the Raman lambda system of a common excited state from which decay to either of two ground states can occur exhibits the asymptotic trapping of population in a superposition of ground states from which it cannot be excited. This is reflected in the Raman absorption lineshape by deep coherence minima or “dark resonances”.^{5} The second example to be discussed concerns the excitation of population from a discrete state to a structured continuum. Again, population can remain in the initial discrete state provided the discrete-continuum excitation rate approaches the structured continuum width. One of the atom-field dressed states then becomes stable, at the expense of an increased decay rate of the other. Laser fluctuations and bandwidths may not entirely dephase population trapping.^{9} These effects demonstrate that close-coupling to a continuum does not always lead to an incoherent irreversible decay.

## Preview

Unable to display preview. Download preview PDF.

## References

- 1.R.M. Whitley and C.R. Stroud Jr., Phys. Rev. A14, 1498 (1976); P.M. Radmore and P.L. Knight, J. Phys. B15, 561 (1982); P.M. Radmore, Phys. Rev. A26, 2252 (1982); P.E. Coleman and P.L. Knight, J. Phys. B15, —1–235 (1982), and J. Phys. B15, 1957 (1982); B.L. Beers and L. Armstrong Jr., Phys. Rev. Al2, 2447 (1975).Google Scholar
- 2.P.E. Coleman, P.L. Knight and K. Burnett, Opt. Comm. 42, 171 (1982).ADSCrossRefGoogle Scholar
- 3.e.g. P.L. Knight, Comments on Atomic and Molecular Physics 10, 267 (1981).Google Scholar
- 4.e.g. P.L. Knight, in “Laser Physics,” D.F. Walls and J.D. Harvey, eds., Academic Press, Sydney (1980).Google Scholar
- 5.G. Alzetta, A. Gozzini, L. Moi and G. Orriols, Nuovo Cim. B36, 5(1976); H.R. Gray, R.M. Whitley and C.R. Stroud Jr., Opt. Lett. 3, 218 (1978); J. E. Thomas, P.R. Hemmer, S. Ezekiel, C.C. Leiby Jr., R.H. Picard and C.R. Willis, Phys. Rev. Lett. 48, 867 (1982).Google Scholar
- 6.D.A. Cardimona, M.G. Raymer and C.R. Stroud Jr., J. Phys. B15, 55 (1982).ADSMathSciNetGoogle Scholar
- 7.P. Lambropoulos, Appl. Opt. 19, 3926 (1980); P. Lambropoulos and P. Zoller, Phys. Rev A24, 379 (1981); K. Rzazewski and J.H. Eberly, Phys. Rev. Lett. 47, 408 (1981); G.S. Agarwal, S.L. Haan, K. Burnett and J. Cooper, Phys. Rev. Lett. 48, 1164 (1982); J.H. Eberly, K. Rzazewski and D. Agassi, Phys. Rev. Lett. 49, 693 (1982); A.I. Andryushin, M.V. Fedorov and A.E. Kazakov, J. Phys. B15, 2851 (1982); P.T. Greenland, J. Phys. B15, 3191 (1982); M. Crance and L. Armstrong Jr., J. Phys. B15, 3199 and 4637 (1982); G.S. Agarwal, S.L. Haan, K. Burnett and J. Cooper, Phys. Rev. A26, 2277 (1982); M. Lewenstein, J.W. Haus and K. Rzazewski, Phys. Rev. Lett. 50, 417 (1982); Z. BialynickiBirula, Phys. Rev. (1983); Y.S. Kim and P. Lambropoulos, Phys. Rev. Lett. 49, 1698 (1982).Google Scholar
- 8.A. Lami and N.K. Rahman, Phys. Rev. A26, 3360 (1982); ibid, Opt. Comm. 43, 383 (1982); A.M.F. Lau, Comments on Atomic and Molecular Physics 11, 249 (1982) and refs. therein.Google Scholar
- 9.B.J. Dalton and P.L. Knight, Opt. Comm. 42, 411 (1982); ibid J. Phys. B15, 3997 (1982); S. Swain, J. Phys. B15, 3405 (1982).ADSGoogle Scholar
- 10.B.J. Dalton and P.L. Knight, Proc. 3rd New Zealand Symposium on Laser Physics, ed. D.F. Walls (1983, to be published).Google Scholar
- 11.L. Armstrong Jr., B.L. Beers and S. Feneuille, Phys. Rev. Al2, 1903 (1975).Google Scholar
- 12.P.M. Radmore and P.L. Knight (to be published).Google Scholar