A method of forming a plasma processing apparatus comprises providing a chamber, the chamber including a wall defining an interior, and a viewport extending through the wall. An analysis apparatus connected to the viewport may be formed. The analysis apparatus includes an analyzer adjacent to the chamber, a probe connected to the analyzer and aligned with the viewport, and a first window aligned with the probe, the first window having a first surface, and a second surface at an opposite side relative to the first surface, the second surface being exposed to the interior of the chamber, and the second surface of the first window has a scattering surface.