The laser beam expanding mirror is used to expand the diameter of the laser beam to reduce the divergence Angle of the laser beam. The laser beam expanding mirror has two main uses: one is to expand the diameter of the laser beam; The second is to reduce the divergence Angle of the laser beam. Therefore, it is used for remote lighting or projection, as well as focusing systems. The divergence Angle of an expanded beam varies inversely to the beam expansion ratio.

Compared with the unexpanded beam, the expanded beam can be focused much smaller. The magnification of the laser beam expanding collimator is the magnification of the beam diameter. The product of the spot size and divergence Angle of the laser beam output from the laser is an optical invariant, which is approximately a certain value. When the waist radius of the beam is expanded x times, its divergence Angle is compressed to the original 1/x, and the compression divergence Angle is actually the collimation of the laser. Compression of divergence Angle does not improve beam quality, which is the product of beam waist radius and divergence Angle. When the divergence Angle of compression is accompanied by the increase of the waist radius, the spot size increases. The laser marking machine is usually used in conjunction with the flat field focusing lens.