## Markovian relaxation processes for atoms in vapors and in solids: calculation of free-induction decay in the weak-external-field limit

JOSA B, Vol. 3, Issue 4, pp. 572-586 (1986)

http://dx.doi.org/10.1364/JOSAB.3.000572

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### Abstract

In a previous paper [
J. Opt. Soc. Am. B3,
564 (
1986)], the validity conditions for the optical Bloch equations were reviewed. It was shown that, even within the limits of an impact or Markovian approximation, the optical Bloch equations fail to account properly for fluctuation-induced changes in atomic transition frequencies. Such changes are properly incorporated in a quantum-mechanical transport equation (QMTE) in which the fluctuation-induced frequency shifts are totally characterized by kernels W(∊′ → ∊) that give the probability density per unit time for a fluctuation to change the frequency shift from ∊′ to ∊. The QMTE describes the interaction of atoms with both an external radiation field and the perturber bath producing the fluctuations. A general method for solving the QMTE as a perturbation series in the external field is presented. Specific calculations are carried out for strong-redistribution, difference [W(∊′ → ∊) is a function of (∊–∊′) only], and Brownian motion kernels. It is shown that, although the kernels possess fundamental differences, they can yield similar results in certain limits. As an example, a perturbation calculation is performed for the free-induction decay (FID) of atoms prepared by a cw laser field and then allowed to radiate when the field is suddenly removed. Radical departures from the predictions of the conventional Bloch equations are found in certain limits, including a first-order contribution to FID in vapors and a nonexponential FID decay for atoms in vapors or solids. The implications of these results to a consistent interpretation of a recent experiment [
Phys. Rev. Lett.50,
1269 (
1983)] on FID in the impurity ion crystal Pr^{3+}:LaF_{3} are explored.

© 1986 Optical Society of America

**History**

Original Manuscript: November 1, 1985

Manuscript Accepted: November 25, 1985

Published: April 1, 1986

**Citation**

P. R. Berman, "Markovian relaxation processes for atoms in vapors and in solids: calculation of free-induction decay in the weak-external-field limit," J. Opt. Soc. Am. B **3**, 572-586 (1986)

http://www.opticsinfobase.org/josab/abstract.cfm?URI=josab-3-4-572

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### References

- P. R. Berman, “Validity conditions for the optical Bloch equations,” J. Opt. Soc. Am. B 3, 564–571 (1986). [CrossRef]
- See, for example, B. W. Shore, “Modeling noise by jump processes in strong laser–atom interactions,” J. Opt. Soc. Am. B 1, 176–188 (1984), which contains extensive references to earlier work. The modeling of frequency fluctuations by jump processes is often attributed to Anderson and Kubo [P. W. Anderson, “A mathematical model for the narrowing of spectral lines by exchange or motion,” J. Phys. Soc. Jpn. 9, 316–339 (1954); R. Kubo, “Note on the stochastic theory of resonance absorption,” J. Phys. Soc. Jpn 9, 935–944 (1954)]. In the optical domain, Burshtein and Oseledchik [A. I. Burshtein, Y. S. Oseledchik, “Relaxation in a system subjected to suddenly changing perturbations in the presence of correlation between successive values of the perturbation,” Sov. Phys. JETP 24, 716–724 (1967)] derive an equation for atomic relaxation resulting from jump processes. [CrossRef]
- G. E. Uhlenbeck, L. S. Ornstein, “On the theory of Brownian motion,” Phys. Rev. 36, 823–841 (1930); see also N. G. Van Kampen, Stochastic Processes in Physics and Chemistry (North-Holland, Amsterdam, 1981); Fluctuation Phenomena, E. W. Montroll, J. L. Lebowitz, eds. (North-Holland, Amsterdam, 1979). [CrossRef]
- See, for example, P. R. Berman, “Theory of collision effects on atomic and molecular lineshapes,” Appl. Phys. (Germany) 6, 283–296 (1975), and references therein; “Collisions in atomic vapors,” in New Trends in Atomic Physics, Les Houches, Session38, 1982, G. Grynberg, R. Stora, eds. (North-Holland, Amsterdam, 1984), pp. 451–514, and references therein; V. P. Kochanov, S. G. Rautian, A. M. Shalagin, “Broadening of nonlinear resonances by velocity-changing collisions,” Sov. Phys. JETP 45, 714–722 (1977); A. G. Kofman, A. I. Burshtein, “Kinetics of Doppler-spectrum saturation,” Sov. Phys. JETP 49, 1019–1026 (1979). [CrossRef]
- A. Schenzle, M. Mitsunaga, R. G. DeVoe, R. G. Brewer, “Microscopic theory of optical line narrowing of a coherently driven solid,” Phys. Rev. A 30, 325–335 (1984). [CrossRef]
- M. Yamanoi, J. H. Eberly, “Relaxation terms for strong field optical Bloch equations,” J. Opt. Soc. Am. B 1, 751–755 (1984). [CrossRef]
- E. Hanamura, “Stochastic theory of coherent optical transients,” J. Phys. Soc. Jpn. 52, 2258–2266 (1983); “Stochastic theory of coherent optical transients. II. Free induction decay in Pr3+:LaF3,” J. Opt. Soc. Jpn. 52, 3678–3684 (1983). [CrossRef]
- J. Javanainen, “Free induction decay in a fluctuating two level system,” Opt. Commun. 50, 26–30 (1984). [CrossRef]
- P. A. Apanasevich, S. Ya. Kilin, A. P. Nizovtsev, “On ‘anomalous’ free induction decay rate,” Opt. Commun. 52, 279–282 (1984). [CrossRef]
- K. Wodkiewicz, J. H. Eberly, “Random-telegraph-signal theory of optical resonance relaxation with applications to free induction decay,” Phys. Rev. A 32, 992–1001 (1985). [CrossRef] [PubMed]
- P. R. Berman, R. G. Brewer, “Modified optical Bloch equations for solids,” Phys. Rev. A 32, 2784 (1985). [CrossRef] [PubMed]
- R. G. DeVoe, R. G. Brewer, “Experimental test of the optical Bloch equations for solids,” Phys. Rev. Lett. 50, 1269–1272 (1983). [CrossRef]
- The resonance approximation consists of neglecting terms that vary as exp[+i(Ω + ω)t]. The field-interaction representation consists of writing ρ12(R, v, t) = ρ12(v, t)exp[−i(k· R− Ωt)].
- S. Chandrasekhar, “Stochastic problems in physics and astronomy,” Rev. Mod. Phys. 15, 1–89 (1943). [CrossRef]
- Note that expression (5.68) lacks the delta-function contribution found in expression (5.23) [compare also expressions (5.58) and (5.7) for Γ ≫ γi]. The Brownian motion model cannot reproduce this delta-function contribution [see A. P. Kolchenko, A. A. Pukhov, S. G. Rautian, A. M. Shalagin, “Effect of selective collisions on the velocity distribution of atoms and on nonlinear interference effects,” Sov. Phys. JETP 36, 619–628 (1973); P. R. Berman, “Brownian motion of atomic systems: Fokker–Planck limit of the transport equation,” Phys. Rev. A 9, 2170–2176 (1974)]. When integrals of Eq. (5.7) or (5.8) or expression (5.23) are taken, the delta-function contribution is negligible, provided that Γ ≫ γi and Γ ≫ ∊0(i.e., in the strict Brownian motion limit when Γ → ∞).
- See, for example, P. R. Berman, “Theory of collision effects on atomic and molecular lineshapes,” Appl. Phys (Germany) 6, 283–296 (1975), and references therein to motional narrowing in atomic and molecular vapors. See also K. Shimoda, “Line broadening and narrowing effects,” in High Resolution Spectroscopy, Vol. 13 of Topics in Applied Physics, K. Shimoda, ed. (Springer-Verlag, Berlin, 1976), pp. 11–49. Motional narrowing in nuclear magnetic resonance dates from earlier times: see, for example, A. Abragam, Principles of Nuclear Magnetism (Oxford U. Press, Oxford, 1961); C. P. Slichter, Principles of Magnetic Resonance (Springer-Verlag, Berlin, 1980), and references therein. [CrossRef]
- P. R. Berman, R. G. Brewer, “Modified Bloch equations for solids,” in Laser Spectroscopy VII, T. W. Hänsch, Y. R. Shen, eds. (Springer-Verlag, Berlin, 1985).
- R. M. Macfarlane, R. M. Shelby, R. L. Shoemaker, “Ultra-high-resolution spectroscopy: photon echoes in YAlO3:Pr3+ and LaF3: Pr3+,” Phys. Rev. Lett. 43, 1726–1730 (1979). [CrossRef]
- P. R. Berman, J. M. Levy, R. G. Brewer, “Coherent optical transient study of molecular collisions: theory and observations,” Phys. Rev. A 11, 1668–1688 (1975). [CrossRef]
- A. G. Yodh, J. Golub, N. W. Carlson, T. W. Mossberg, “Optically inhibited collisional dephasing,” Phys. Rev. Lett. 53, 659–667 (1984). [CrossRef]

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