Figure 3.
Optical two beam deflection technique. (a) Sketch of the set-up. The substrate of length ℓ, width w, and thickness ts is fixed along its width at the top end. The curvature 1/R of the substrate is monitored by reflecting two laser beams onto position sensitive detectors. (b) Set-up mounted to a window flange of an UHV chamber, the substrate is located inside of the chamber, behind the window. 1: laser, 2: lenses for beam focusing, 3: beam splitter, 4: mirrors, 5: position sensitive detector (split-photodiode).