The spot output from the optical fiber is generally a circular spot with a certain divergence angle. The specific spot size is related to the fiber core diameter, and the divergence angle is determined by the fiber numerical aperture. The common optical fibers are divided into single mode and multimode, the diameter of single mode core is μm from 2.9 to 9μm, the diameter of multimode core is μm from 50 to 400μm, and the numerical aperture is generally 0.15 NA and 0.22 NA. respectively The numerical aperture refers to the sinusoidal value of the maximum incident angle of the total reflection transmission of the beam in the fiber. It can be simply regarded as the divergence angle of the laser fiber .0.22 NA representing the divergence angle (half angle) about 12.5° and 0.15 NA representing the divergence angle about 8°.