Observatoire de Meudon, Salle de Conférences du Château
The Sun as a laboratory for quantum physics
Jan OLOF STENFLO
Institute of Astronomy, ETH Zurich
Résumé :
With the advent of highly sensitive imaging polarimeters
an entirely new "spectral face" of the Sun in linear
polarization has become accessible to exploration.
It is due to coherent scattering processes, which
produce a spectrum that is as richly structured
as the ordinary intensity spectrum but with spectral
structures that look entirely different and that
have different physical origins. The work on trying
to identify these various, previously unfamiliar
structures has led to new insights in atomic and
quantum physics. We find spectral signatures of
various types of quantum interferences, hyperfine
structure, and optical pumping. The molecular lines,
which are very weak and next to invisible in the
intensity spectrum, stand out with high contrast
in this so-called "Second Solar Spectrum".
There are also structures that have remained enigmatic
for more than a decade, an example being the observed
polarization peak in the D1 line of sodium. According
to quantum mechanical predictions this line should
be intrinsically unpolarizable. To determine whether
this is a problem of solar physics or of quantum physics
we have set up a laboratory experiment to explore the properties
of polarized D1 scattering under controlled conditions
and in well defined magnetic fields. This experiment
has produced unexpected results that are unequivocally
at odds with our current understanding of quantum scattering.
The second solar spectrum has also given us a diagnostic
tool that allows us to explore aspects of solar magnetism
that have been inaccessible to the Zeeman effect.
Thereby vast amounts of "hidden" magnetic flux in
the photosphere has been uncovered, which has led to
a new view of the nature of solar magnetism.
