Abstract

A new spectroscopic technique for studying adsorption of atoms at a transparent dielectric surface is exploited. A quantitative comparison of the Autler-Townes splitting in measured and calculated, surface temperature-dependent two-photon evanescent wave spectra provides values of the adsorption energy, the preexponential factor for the rate of desorption and the polarizability of alkali atoms, adsorbed on a glass surface. It is speculated that this technique could form the basis for future two-photon control of atoms close to dielectric surfaces.

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References

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  1. V.M. Agranovich and D.L. Mills, Eds., Surface Polaritons (North-Holland, Amsterdam, 1982).
  2. A. Lindinger, M. Verbeek and H.-G. Rubahn, "Adiabatic population transfer by acoustooptically modulated laser beams," Z. Phys. D 39, 93-100 (1997).
    [CrossRef]
  3. C. Delsart and J.-C. Keller, "The optical Autler-Townes effect in Doppler-broadened three-level systems," J. Phys. (Paris) 39, 350-360 (1978).
    [CrossRef]
  4. V.G. Bordo and H.-G. Rubahn, "Two-photon evanescent wave spectroscopy of alkali atoms," Phys. Rev. A, submitted.
  5. R. Salomaa and S. Stenholm, "Two-photon spectroscopy: effects of a resonant intermediate state," J. Phys. B: Atom. Molec. Phys. 8, 1795-1805 (1975).
    [CrossRef]
  6. R. Salomaa and S. Stenholm, "Two-photon spectroscopy II. Effects of residual Doppler broadening," J. Phys. B: Atom. Molec. Phys. 9, 1221-1235 (1976).
    [CrossRef]
  7. A.M. Bonch-Bruevich, Yu.M. Maksimov and V.V. Khromov, "Variation of the absorption spectrum of sodium atoms when they are adsorbed on a sapphire surface" Optics Spectrosc. 58, 854-856 (1985).
  8. S. Gozzini, G. Nienhuis, E. Mariotti, G. Pa_uti, C. Gabbanini and L. Moi, "Wall effects on light-induced drift," Optics Commun. 88, 341-346 (1992).
    [CrossRef]
  9. V.P. Zhdanov, Ya. Pavlichek and Z. Knor, "'Normal' preexponential factors for elementary physical-chemical processes at a surface," Surface 10, 41-46 (1986) (in Russian).

Other

V.M. Agranovich and D.L. Mills, Eds., Surface Polaritons (North-Holland, Amsterdam, 1982).

A. Lindinger, M. Verbeek and H.-G. Rubahn, "Adiabatic population transfer by acoustooptically modulated laser beams," Z. Phys. D 39, 93-100 (1997).
[CrossRef]

C. Delsart and J.-C. Keller, "The optical Autler-Townes effect in Doppler-broadened three-level systems," J. Phys. (Paris) 39, 350-360 (1978).
[CrossRef]

V.G. Bordo and H.-G. Rubahn, "Two-photon evanescent wave spectroscopy of alkali atoms," Phys. Rev. A, submitted.

R. Salomaa and S. Stenholm, "Two-photon spectroscopy: effects of a resonant intermediate state," J. Phys. B: Atom. Molec. Phys. 8, 1795-1805 (1975).
[CrossRef]

R. Salomaa and S. Stenholm, "Two-photon spectroscopy II. Effects of residual Doppler broadening," J. Phys. B: Atom. Molec. Phys. 9, 1221-1235 (1976).
[CrossRef]

A.M. Bonch-Bruevich, Yu.M. Maksimov and V.V. Khromov, "Variation of the absorption spectrum of sodium atoms when they are adsorbed on a sapphire surface" Optics Spectrosc. 58, 854-856 (1985).

S. Gozzini, G. Nienhuis, E. Mariotti, G. Pa_uti, C. Gabbanini and L. Moi, "Wall effects on light-induced drift," Optics Commun. 88, 341-346 (1992).
[CrossRef]

V.P. Zhdanov, Ya. Pavlichek and Z. Knor, "'Normal' preexponential factors for elementary physical-chemical processes at a surface," Surface 10, 41-46 (1986) (in Russian).

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Figures (6)

Figure 1.
Figure 1.

a) Na term scheme, relevant to the present two-photon experiments. Laser 1 excites the atoms from the 3S to the 3P state, while laser 2 excites them from the 3P to the 5S state. b) Experimental set up. Na atoms are emitted from a Na dispenser inside a vacuum apparatus, where they hit a prism surface (T S = 220–300 K). The two counterpropagating lasers illuminate the prism under an angle larger than the critical angle θc , and thus Na atoms are excited in the evanescent wave into the 5S-state, from which they fluoresce back into the ground state. The fluorescence is collected by a photomultiplier behind an interference filter, tuned to the (4P → 3S) transition.

Figure 2.
Figure 2.

Two-evanescent wave fluorescence spectrum obtained by tuning the frequency of laser 1 (P=42 mW) and setting the frequency of laser 2 (P=20 mW) fixed to 16227.17 cm -1.

Figure 3.
Figure 3.

Dependence of measured two-photon splitting on the prism temperature. Laser 1 (P=35 mW) was scanned, while laser 2 (P=4mW) was set at a fixed frequency of 16227.20 cm -1. The error bars result from the laser linewidth.

Figure 4.
Figure 4.

Comparison of the two-photon fluorescence theory (grey line) with an experimentally determined spectrum at a surface temperature of 291 K. Laser parameters same as in Fig.3.

Figure 5.
Figure 5.

a) The dependence of the calculated relative EW intensity, η, on the prism surface temperature. The solid grey line shows a fit by the Langmuir model of adsorption. b) Dependence of μ, on the inverse surface temperature. The solid line is a linear fit with a slope 2Q/k= 18600 K.

Figure 6.
Figure 6.

The calculated dependence of the surface coverage on the surface temperature.

Equations (14)

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j = i ω 4 π ( 1 + 4 π N s α s ) E t ,
E 2 = 2 k 0 z k 0 z + k 2 z 4 πi ( ω c ) 2 N s α s E 0 ,
k 0 z = ω c ϵ 1 cos θ 0
k 2 z = ω c ϵ 2 ϵ 1 sin 2 θ 0
E 2 = 2 1 i 4 π ϵ 1 cos θ c ω c N s α s E 0 .
θ = N s N 0 .
JS ( 1 θ ) = N 0 θ w ,
w = v exp ( Q kT )
θ ( T ) = 1 1 + A exp ( Q kT ) ,
A = N 0 v JS .
η ( T ) = E 2 ( T ) E 2 ( ) 2 = 1 1 + B θ 2 ( T ) ,
B = ( 4 π ϵ 1 cos θ c ω c α s N 0 ) 2 .
η ( T ) = 1 1 + B A 2 exp ( 2 Q kT ) .
μ ( T ) = ln ( 1 η ( T ) 1 )

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