Device/system and treatment method of varicose veins and other vein abnormalities are presented. Treatment A comprises combining two wavelengths to occlude abnormal veins. Wavelengths are chosen as effective absorption peaks of hemoglobin and/or water, e.g. 980 nm and 1460 nm. Irradiations of blood, collagen and water in the vessel cause occlusion/shrinkage. Constant power-density is used based on fiber withdrawal speed and structural vein parameters. Treatments employ dual laser wavelengths or highly-controlled vein-wall damage wavelengths. Monitored control parameters and predetermined vein structural parameters. Alternatively, 1460+60 nm laser energy is employed, having high absorption in the vein wall, creating little thermal stress outside the vein, and being effective in initiating damage reaction response. Treating at 1460+60 nm has benefits of high vein closure rates and favorable post-operative results, i.e., little post-operative pain/discomfort, brusing/inflammatory reactions, due to their very high absorption in small volumes of the collagen/water in vein walls.