where Q_0 is the total power input, R_c is the reflection coefficient, A_c is the absorption coefficient, σ_x,σ_y is the standard deviation parameters, e^(-[(x-x_0 )^2/(2σ_x^2 )+(y-y_0 )^2/(2σ_y^2 )]) is the 2D Gaussian distribution in x-y plane, e^(-A_c z) is the exponential decay due to absorption.