Home/Technical Glossary/Single Mode Single Mode Lasers are said to operate in either “single mode” or “multi-mode.” Single mode fiber lasers are typically delivered via fiber with a core diameter of around 9 microns producing a narrow, high intensity beam which can be focused down to a spot size as small as 10 microns. This high intensity, small spot is ideally suited for laser cutting applications, but generally not great for welding, as weld widths are too narrow to accommodate most production fit-up tolerances. For more information, read our blog Fiber Laser Micro Welding: Single Mode or Multi Mode?