What gas do Fibre lasers use
Refraction bends light in an optical fiber laser. The optical fiber cable passes light through an opaque silica glass core that is impure and transparent. Cladding is a layer of silica that has been doped with other materials to reduce its refractiveindex. The core-clad interface will reflect light due to the difference in their refractive index.
For engraving larger areas, you will need a 30-W or 50W laser fiber to upgrade to 7.87"x7.87", or 11.81"x11.87".