The beam expander also has a collimating function, but the beam expander is aimed at the beam (beam with a certain divergence angle). Many lasers on the market emit light beams, such as CO2 glass tubes, CO2 radio frequency tubes, lamp-pumped YAG lasers, lasers from QBH fiber lasers, end-pumped 355nm 532nm 1064nm lasers. The light from these lasers are all beams, and they are not strictly parallel light (when the beam quality M2 of a laser is 1, the light of this laser has no divergence angle, but this can only be an ideal state. It does not exist in real life. Generally, the M2 coefficient of lasers on the market can reach 1.2, which is already very good).
Why the beam expander can play the role of collimation? Everyone knows that the beam expander can expand the beam, in professional terms, it expands the beam waist radius. The product of the beam waist radius and the divergence angle of the laser is a fixed value, and the increase in the beam waist radius (ie beam expansion) will reduce the divergence angle (to achieve collimation). There is a conclusion that after passing through an N-fold beam expander, the divergence angle of the laser beam is reduced to one-Nth of the original. For example, after a 4-fold beam expander, the divergence angle is reduced to 1/4 of the original. This is why we try to use a larger beam expander as much as possible (provided that the size of the beam after passing through the beam expander does not exceed the size of the galvanometer spot).
The collimator includes: the collimator of the fiber welding machine and the collimator of the fiber cutter, the beam expander includes: CO2 beam expander, 532nm beam expander, 355nm beam expander, 1064nm beam expander, and 650nm beam expander.