Abstract: The invention provides a polishing pad for chemical-mechanical polishing comprising (a) a first polishing layer comprising a polishing surface and a first aperture having a first length and first width, (b) a second layer comprising a body and a second aperture having a second length and second width, wherein the second layer is substantially coextensive with the first polishing layer and at least one of the first length and first width is smaller than the second length and second width, and (c) a substantially transparent window portion, wherein the transparent window portion is disposed within the second aperture of the second layer so as to be aligned with the first aperture of the first polishing layer and the transparent window portion is separated from the body of the second layer by a gap. The invention further provides a chemical-mechanical polishing apparatus and method of polishing a workpiece.