Focusing Your Laser 101 with J Tech Photonics, Inc.
Principle of laser focus displacement meter. | Download Scientific Diagram
If laser processes are from a few percent to maybe 20 percent, why not skip the laser part and just collimate focus the source light directly, for burning and cutting? - Quora
Graveur laser Ortur Laser Master 2 Pro : modules laser à longue focale – Buybestgear