End facet protection for light sources and methods for metrology applications

A system and method for providing a light source is disclosed. In one arrangement, the light source comprises: a gas chamber having a window; an optical fiber, the optical fiber being hollow and having an axial direction, an end portion of the optical fiber being enclosed within the gas chamber and optically coupled to the window via an optical path; and a surface disposed around the end of the optical fiber and extending through the end of the optical fiber in the axial direction toward the window so as to limit one or more of: an exchange of gas between the optical path and a remainder of the gas chamber; entry of plasma towards or into the optical fiber; and a free radical flux toward the etch-sensitive surface. 公开一种用于提供光源的系统和方法。在一个布置中，所述光源包括：气室，所述气室具有窗口；光纤，所述光纤是中空的且具有轴向方向，所述光纤的端部被封闭于所述气室内且经由光学路径光学地耦合至所述窗口；以及表面，所述表面围绕所述光纤的所述端部设置，并且在所述轴向方向上朝向所述窗口延伸通过所述光纤的所述端部，以便限制以下中的一个或更多个：所述光学路径与所述气室的其余部分之间的气体的交换；等离子体朝向所述光纤或至所述光纤中的进入；以及朝向蚀刻敏感表面的自由基通量。