Parameters
wox: half width of the beam waist in the XZ plane
woy: half width of the beam waist in the YZ plane
lam: wavelength
M2x: M square factor (M2) in the XZ plane
M2y: M square factor (M2) in the YZ plane
x: coordinate along the X axis
y: coordinate along the Y axis
z: distance from the waist to the plane perpendicular to the beam axis
P: power of the laser beam
Imax : on-axis intensity at the distance z from the waist
Ixy : intensity at the point with the coordinates x and y in the plane at the distance z from the waist
