Laser spectroscopy of gaseous atoms in local field
using optical forbidden transitions
S Tojo1
1
Department of Physics, Chuo University, 1-13-27 Kasuga, Bunkyo, Tokyo 112-8551, Japan
Laser spectroscopy in a local field is one of powerful techniques to investigate interactions among
atoms, molecules, and matters: reflection spectroscopy for observation of atom-surface interactions [1],
and photoassociation spectroscopy of ultracold atoms for measurement of localized diatomic and
molecular interactions [2]. The localized matter can generate large field gradient owing to the
considerably localized light filed near the surface and van der Waals potentials between atoms.
Optical forbidden transitions are well-known for application of precision spectroscopy such as atom
clocks due to narrow spectra [3]. However, since an interaction area of a local field for atoms is
appreciably smaller than that of free space, it is extremely difficult to observe spectra using forbidden
transitions with a small transition rate less than 10-6. Therefore, optical forbidden transitions had been
out of target for use in local field measurements. Nevertheless, higher-order interactions such as
electric and magnetic multipole moments and spin-orbital interactions in optical forbidden transitions
can be of interest because such transitions are sensitive to field inhomogeneity.
We have experimentally investigated optical forbidden transitions of atoms in local fields. We have
found enhanced oscillator strength of an electric quadrupole transition of cesium atoms with an
evanescent field depending on an angle of incidence of light using attenuated total reflection
spectroscopy [4] as shown in Fig. 1(a). In the case of a spin-forbidden transition, we have measured
interatomic interactions using laser-cooled ytterbium atoms in photoassociation spectroscopy [5] in Fig.
1(b). Due to its narrow transition line, we have found different diatomic interactions between different
isotopes due to different local fields. We will also report on new experimental and calculation results
with hot and cold atoms in local fields [6, 7].
(a)
(b)
Figure 1. (a) Ratio of line strengths of an electric quadrupole transition of 133Cs atoms
in an evanescent field between experiment and calculation with a fixed transition
strength depending on relative incident angle δ from the critical angle. (b) Partial-wave
potential as a function of interatomic distance and the reconstructed squared wave
functions in ultracold 174Yb (open circles) and 176Yb (closed triangles) atoms.
References:
[1] Ducloy M, in Nanoscale Science and Technology, edited by N. Garcia et al., (Kluwer, Dordrecht, 1998)
[2] Jones K M, Tiesinga E, Lett P D, Julienne P S 2006 Rev. Mod. Phys. 78 483
[3] Takamoto M, Hong F-L, Higashi R, Katori H 2005 Nature 435 321
[4] Tojo S, Hasuo M, Fujimoto T 2004 Phys. Rev. Lett. 92 053001
[5] Tojo S, Kitagawa M, Enomoto K, Kato Y, Takasu Y, Kumakura M, Takahashi Y 2006 Phys. Rev. Lett. 96 153201
[6] Tojo S, Shibata K, Bloch D 2016 submitted
[7] Yatsui T, Tsuboi T, Yamaguchi M, Nobusada K, Tojo S, Stehlin F, Soppera O, Bloch D 2016 Light Sci. Appl. 5
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