A device/system and a method for the treatment of varicose veins and other vein abnormalities are presented. In one preferred embodiment, the treatment comprises a combination of two wavelengths to effectively occlude abnormal veins. The wavelengths are chosen as the effective absorption peaks of hemoglobin and water, which are seen at these wavelengths, approximately 980 nm and 1460 nm respectively. The vein is targeted with these wavelengths to obtain maximum and effective absorption. The Near Infra Red laser radiations are delivered to blood, collagen and water in the vessel which results in occlusion and shrinkage of the vein. In this technique an optical fiber is inserted into the vein and laser sources are used to irradiate the vein. A control mechanism allows delivery of constant power density based on feedback about speed of fiber withdrawal and local structural vein parameters. This technique is an effective treatment for vein disorders as the treated vein is targeted with dual wavelengths of energy or alternatively with a wavelength having highly controlled vein-wall damage character. The treatment conditions are based on feedback from different control parameters that are monitored and preliminary predetermined structural parameters of the treatment site. The device involves a side firing optical fiber which can also irradiate nearly uniform circumferentially from said fiber's distal end. Alternatively, in another preferred embodiment 1460+60 nm laser energy is employed, which with its high absorption in the vein wall, creates little thermal stress outside the vein, and is very effective in initiating the damage reaction response, shrinkage in the vein wall. An example is using, e.g., a 1470±20 nm wavelength. Laser vein treatments administered using 1460 ± 60 nm have the benefits of high vein closure rates and extremely favorable post-operative results, i.e., little, if any, post-operative pain/discomfort, brusing or inflammatory reactions, due to their v
