Laser spectroscopy experiments are often conducted with a probe that does not significantly alter the medium’s properties. For a two-level atom a clear measure of the strength of a probe beam in terms of the saturation intensity is known. We show that for a multilevel atom the situation is very different, and the effects of optical pumping are crucial to understanding the opacity of the medium. We present a simple theoretical analysis for Doppler-broadened spectroscopy of alkali metals on the line that emphasizes the importance of the transient nature of the population dynamics, and the crucial role of the distribution of the times of flight of atoms through the probe beam. Experimental results are obtained with room temperature rubidium vapor probed by an extended-cavity diode laser and confirm our theoretical prediction.
REFERENCES
1.
K. B.
MacAdam
, A.
Steinbach
, and C.
Wieman
, “A narrow-band tuneable diode laser system with grating feedback, and a saturated absorption spectrometer for Cs and Rb
,” Am. J. Phys.
60
, 1098
–1111
(1992
).2.
D. A.
Van Baak
, “Resonant Faraday rotation as a probe of atomic dispersion
,” Am. J. Phys.
64
, 724
–735
(1996
).3.
D. W.
Preston
, “Doppler-free saturated absorption: Laser spectroscopy
,” Am. J. Phys.
64
, 1432
–1436
(1996
).4.
C.
Leahy
, J. T.
Hastings
, and P. M.
Wilt
, “Temperature dependence of Doppler-broadening in rubidium: An undergraduate experiment
,” Am. J. Phys.
65
, 367
–371
(1997
).5.
D.
Budker
, D. J.
Orlando
, and V.
Yashchuk
, “Nonlinear laser spectroscopy and magneto-optics
,” Am. J. Phys.
67
, 584
–592
(1999
).6.
K.
Razdan
and D. A.
Van Baak
, “Demonstrating optical saturation and velocity selection in rubidium vapor
,” Am. J. Phys.
67
, 832
–836
(1999
).7.
C. J.
Vale
, M. R.
Walkiewicz
, P. M.
Farrell
, and R. E.
Scholten
, “One-dimensional laser cooling of an atomic beam in a sealed vapor cell
,” Am. J. Phys.
70
, 71
–75
(2002
).8.
D. A.
Smith
and I. G.
Hughes
, “The role of hyperfine pumping in multilevel systems exhibiting saturated absorption
,” Am. J. Phys.
72
, 631
–637
(2004
).9.
A. J.
Olson
, E. J.
Carlson
, and S. K.
Mayer
, “Two-photon spectroscopy of rubidium using a grating-feedback diode laser
,” Am. J. Phys.
74
, 218
–223
(2006
).10.
K. G.
Libbrecht
and M. W.
Libbrecht
, “Interferometric measurement of the resonant absorption and refractive index in rubidium gas
,” Am. J. Phys.
74
, 1055
–1060
(2006
).11.
12.
M. L.
Harris
, C. S.
Adams
, S. L.
Cornish
, I. C.
McLeod
, E.
Tarleton
, and I. G.
Hughes
, “Polarization spectroscopy in rubidium and cesium
,” Phys. Rev. A
73
, 062509
–1
(2006
).13.
H. J.
Metcalf
and P.
van der Straten
, Laser Cooling and Trapping
(Springer
, New York
, 1999
), Chap. 2.14.
15.
J.
Sagle
, R. K.
Namiotka
, and J.
Huennekens
, “Measurement and modelling of intensity dependent absorption and transit relaxation in the cesium line
,” J. Phys. B
29
, 2629
–2643
(1996
).16.
P. G.
Pappas
, M. M.
Burns
, D. D.
Hinshelwood
, M. S.
Feld
, and D. E.
Murnick
, “Saturation spectroscopy with laser optical pumping in atomic barium
,” Phys. Rev. A
21
, 1955
–1968
(1980
).17.
G.
Moon
and H.-R.
Noh
, “Observation of nonstationary effects in saturation spectroscopy
,” Opt. Commun.
281
, 294
–298
(2008
).18.
A. S.
Arnold
, J. S.
Wilson
, and M. G.
Boshier
, “A simple extended-cavity diode laser
,” Rev. Sci. Instrum.
69
, 1236
–1239
(1998
).19.
P.
Siddons
, C. S.
Adams
, Chang
Ge
, and I. G.
Hughes
, “Absolute absorption on rubidium D lines: Comparison between theory and experiment
,” J. Phys. B
41
, 155004
–1
(2008
).20.
W.
Gawlick
, “Nonstationary effects in velocity-selective optical pumping
,” Phys. Rev. A
34
, 3760
–3769
(1986
).21.
E.
Pfleghaar
, J.
Wurster
, S. I.
Kanorsky
, and A.
Weis
, “Time of flight effects in nonlinear magneto-optical spectroscopy
,” Opt. Commun.
99
, 303
–308
(1993
).22.
A. V.
Taichenachev
, A. M.
Tumaikin
, V. I.
Yudin
, M.
Stähler
, R.
Wynands
, J.
Kitching
, and L.
Hollberg
, “Nonlinear-resonance line shapes: Dependence on the transverse intensity distribution of a light beam
,” Phys. Rev. A
69
, 024501
–1
(2004
).23.
C.
Wieman
and T. W.
Hänsch
, “Doppler-free laser polarization spectroscopy
,” Phys. Rev. Lett.
36
, 1170
–1173
(1976
);C. P.
Pearman
, C. S.
Adams
, S. G.
Cox
, P. F.
Griffin
, D. A.
Smith
, and I. G.
Hughes
, “Polarization spectroscopy of a closed atomic transition: Applications to laser frequency locking
,” J. Phys. B
35
, 5141
–5151
(2002
).24.
L. P.
Maguire
, R. M.W.
van Bijnen
, E.
Mese
, and R. E.
Scholten
, “Theoretical calculation of saturated absorption spectra for multi-level atoms
,” J. Phys. B
39
, 2709
–2720
(2006
).© 2009 American Association of Physics Teachers.
2009
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