The diode laser systems emit light from their emitters which is not collimated in their vertical and horizontal axis (Figure 1). In com- parison, the divergence in the y-axis is significantly higher than the divergence in the x-axis.
Due to this observation, the y-axis is called fast-axis while the x-axis is called slow- axis. High power diode manufacturer provide specifications for the divergence distribution of the lasers.
In common laser system, only a convex lens is used to zoom the laser beam, resulting in the rectangular laser spot, like AtomStack A5 and many other laser engravers from other brands, however in high-end laser engravers, such as AtomStack A5 pro, A5 M30 and A5 M40, besides convex lens, an additional lens called Fast-Axis-Collimating Lens is used.
FAC lens is an optical lens that collimates light spreading from a semiconductor laser (LD) in the fast-axis direction (Figure 2). LD have a large divergence angle in the fast-axis direction, so the output light cannot be efficiently used unless collimated. The FAC lens collimates light spreading from a LD into a narrow beam with a radiation angle of several milliradians (mrad) or less so that the diverging light can be efficiently utilized.