An arc lamp having window flange with slots has been disclosed. The arc lamp may include a reflector body having a circular rim at one end to define an opening, the circular rim having an outer diameter and an inner diameter and a window flange including a surface having a first end and a second end, the first end defining a circle having a diameter larger than the inner diameter of the circular rim of the reflector body, and the surface being brazed to the circular rim along at least a portion of the first end, wherein the window flange further includes a second surface extending from the first end of the first surface to define a plurality of slots. The arc lamp may further include a window mounted to the window flange near the second end of the window flange.