What is the effect of laser beam expander?

Laser beam expander has two main uses: one is to expand the diameter of the laser beam; the other is to reduce the divergence angle of the laser beam. Therefore, it is used for long distance illumination or projection, as well as focusing system. The divergence angle of a bundle of beams is proportional to the expansion ratio. Compared with the unexpanded beam, the beam after beam expansion can be focused smaller. The magnification of laser beam expanding collimator is the magnification of beam diameter. The product of the spot size and divergence angle of the laser beam output from the laser is an optical invariant, approximating a certain value. When the beam waist radius increases by X times, the divergence angle is reduced to 1/x of the original one. The divergence angle is actually the collimation of the laser. Compression of divergence angle can not improve beam quality, beam quality is the product of waist radius and divergence angle; compression of divergence angle at the same time will accompany the increase of waist radius, the spot size increases. The focal laser lens is often used in laser marking machine.