  The optical properties of plasmas with high densities and medium temperatures
are analyzed by the use of a free electron model with Fermi-Dirac statistics.
For the present collisional plasma the frequency of electron-ion collision is
very large relative to the optical and infra-red frequencies. A quantum
mechanical equation for the frequency of collisions is developed by the use of
Fermi-Dirac statistics and Rutherford scattering theory. The validity of the
Rutherford scattering theory is discussed. The influence of many weak
collisions is taken into account by a Coulomb logarithmic function. The present
analysis might have implication to stellar plasmas with medium temperatures for
which Fermi-Dirac statistics is used. The relations between the present
analysis and the stabilities of stars plasmas are discussed. The ratio between
the radius and mass of star plasmas with the present densities and that of a
typical white dwarf are discussed.
