https://doi.org/10.1140/epjd/e2002-00176-1
Magnetic field effects on the 1 083 nm atomic line of helium
Optical pumping of helium and optical polarisation measurement in high magnetic field
1
Laboratoire Kastler Brossel (Laboratoire de l'Université Pierre et Marie Curie et de l'École Normale Supérieure,
associé au Centre National de la Recherche Scientifique (UMR 8552)) ,
24 rue Lhomond, 75231 Paris Cedex 05, France
2
Marian Smoluchowski Institute of Physics, Jagiellonian University, ul. Reymonta 4, 30-059 Kraków, Poland
Corresponding author: a nacher@lkb.ens.fr
Received:
23
March
2002
Published online:
24
September
2002
The structure of the excited and
triplet states of
and
in an applied magnetic field B is
studied using different approximations of the atomic Hamiltonian. All optical
transitions (line positions and intensities) of the 1 083 nm
–
transition are computed as a function of B. The effect
of metastability exchange collisions between atoms in the ground state and in the
metastable state is studied, and rate equations are derived, for the
populations these states in the general case of an isotopic
mixture in an arbitrary field B. It is shown that the usual spin-temperature
description remains valid. A simple optical pumping model based on these rate
equations is used to study the B-dependence of the population
couplings which result from the exchange collisions. Simple
spectroscopy measurements are performed using a single-frequency laser diode
on the 1 083 nm transition. The accuracy of frequency scans and of
measurements of transition intensities is studied. Systematic experimental
verifications are made for B=0 to 1.5 T. Optical pumping effects resulting
from hyperfine decoupling in high field are observed to be in good agreement
with the predictions of the simple model. Based on adequately chosen absorption measurements at
1 083 nm, a general optical method to measure
the nuclear polarisation of the atoms in the ground state in an arbitrary field
is described. It is demonstrated at
T, a field for which the usual
optical methods could not operate.
PACS: 32.60.+i – Zeeman and Stark effects / 32.70.-n – Intensities and shapes of atomic spectral lines / 32.80.Bx – Level crossing and optical pumping
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2002