Calculation method of laser divergence angle

Firstly, adjust the laser light to parallel light
to measure distant light spot and light spot at aperture

Divergence angle =2arctan ((spot diameter- beam diameter at aperture) / 2 / distance) * 1000All units are mm     

For convenience’s sake, you can use the following simple formula
(spot diameter (mm) – beam diameter at aperture (mm))/ distance (m)

Note: the above formula adopts the radian calculation result, the unit is mrad, if using the angle calculation result, please take ×π/180 as the unit
If it is 445nm laser, as all spots are rectangular and have big divergence in ⊥ direction, the beam diameter at aperture is the short side to measure spots at aperture while the beam diameter at aperture is the long side, the same for 635nm laser