  A plasma under the influence of an external magnetic field changes the
optical properties due to the Zeeman splitting of the energy levels. This
splitting degenerates an initial single spectral line into a system of spectral
lines with different transition frequencies defined by the electronic structure
of the energy levels. Newly created magnetic sub-levels redefine the spectral
profile of the line emission and therefore radiation transport mechanism in
optically thick plasma. Self-absorption which defines the excited
state-densities is an important mechanism and can be used with other methods to
describe the state densities for an optically thick plasma. This method is an
established tool to retrieve state-density and plasma parameters. To measure
each magnetic sub-level density of argon 1s4 and 1s5 (in Paschen's notation) a
tunable diode laser absorption spectroscopy (TDLAS) was used. Based on
reconstructed excited state densities, the self-absorption coefficient was
calculated for individual magnetic sub-levels. A decrease in self-absorption
with an external magnetic field was noticed indicating a higher transparency of
the plasma. Furthermore a polarization dependent self-absorption was found. The
presented results can help to model optical properties and interpret the
absorption of a low-pressure optically thick magnetized plasma.
