 Based on the semi-classical radiation absorption theory within the electric dipole approximation, the electric vector of the circularly polarized waves propagates along the +z direction.In this system, formula_6 is the angular frequency, and formula_7 = n – ik is the complex refractive index.As the light travels, the attenuation of the beam is expressed as

where formula_9 is the intensity of light at position formula_10, formula_11 is the absorption coefficient of the medium in the formula_10 direction, and formula_13 is the speed of light.