Apparent emitting properties of semitransparent medium layer with specular semitransparent surface and opaque diffuse substrate

Based on the internal emission of the medium, the pseudo-source adding method was applied to investigate the apparent spectral emission of a semitransparent medium layer with semitransparent specular surface and opaque diffuse substrate. An analytical expression was derived for the apparent directional and hemispherical emissivity. The factors affecting the apparent emission of the medium layer with respect to the optical thickness, the refractive index of the medium and the reflectivity of substrate were studied. The results show that the refractive index has great influence on the directional emission of the medium. Combined with the other factors, it causes the directional emission to appear complicated anisotropy.