The inverse bremsstrahlung absorption is one of the most absorption processes in inertial confinement fusion plasma. In the present work, some important optical properties of plasma, such as index of refraction, absorption coefficient, electrical conductivity, and the electrical dielectric function in degenerate conditions are presented from an average atom model's point of view. To include quantum diffraction effects, the Coulomb potential is replaced by an effective quantum potential for a screened electron-ion interaction, named Klebg potential. Therefore, the electrical conductivity contribution of the free-free electrons absorption that is inverse of the bremsstrahlung absorption, for transition from state i to state j is obtained using the wave function of this potential. By this method, the effect of degenerate plasma on the inverse bremsstrahlung power is calculated using the free-free absorption coefficient. Finally, the obtained results of the free-free optical opacity of plasma and the inverse bremsstrahlung absorption power from classical and degenerate plasma are compared.
• In low photon energy, the electrons of plasma absorb the photon energy and transfer to upper levels of energy.
• In high photon energy, the absorption coefficient is smaller than the refraction coefficient.
• The plasma is optically thin in high photon energy, and the photon escapes from the plasma.
• In low photon energy, plasma is optically thick, therefore the photon is absorbed by electrons of the plasma.
• The degeneracy has caused a reduction in opacity and the inverse bremsstrahlung absorption.