The hollow waveguide path (1) has a hollow glass fiber tube (10) whose outer side is provided with silver thin layer (30) and dielectric thin layer (40). A protective layer (20) is provided between glass fiber tube and silver thin layer, and is formed before silver mirror reaction for forming sliver thin layer. The dielectric thin layer is formed by organic material, and the protective layer is formed by inorganic material. An independent claim is included for laser treatment tool.