nniicckk78, the fiber mode is a TEM00 vs a TEM01 (it is a solid spot vs. a donut shape). Shooting a mode shot at the head is the best way to tell you what exactly is going on with your beam from the lens - down. These fiber lasers are very picky. ANY dust or debris on the lens or protective window, and you're done! Any time you remove the lens cartridge from the cutting head, and you run the risk of exposing it to any dust particles floating around your shop - I don't care how clean you think you're being, it WILL happen. The OEM sells said acrylic for something like $60 a 3/8" x 4" x 4" pc, and we can get 18 shots (9 per side) out of it. It becomes very expensive very quick.
As a followup, I have found an alternative, and was very pleased with the results. If anyone would like to purchase some , PM me and I can get you the info.