Polarized heterodyne astigmatic sensing technique for measurement of discontinuous surface

An approach based on laser polarizing heterodyne astigmatic principle was proposed for absolute tracing measurement of discontinuous surfaces. The approach proposed uses the shape of reflected polarized light of the object received from two detectors, which are placed at the same distance before and behind the focal plane of two cylindrical lenses, and uses the focal error signal obtained through the heterodyne subtraction of two signals received from two detectors and the normalization of the intensity, to achieve absolute measurement and aiming trigger of discontinuous 3D surfaces. In a polarized heterodyne astigmatic sensor, the introduction of polarized incident light and light splitting of polarized beam splitter can effectively suppress the undesired influence on measurements caused by the disturbance of the laser source in intensity and multi-reflection among optical elements, and obviously improve the anti-interference capability and linearity of heterodyne astigmatic defocused measurement. Experimental results indicate that the optical sensor has a resolution of better than 0.005 μm and it can measure the surface with tilt angle of 20°, while the it has a measurement range of ±10 μm.