Non-contact Measurement Technique for Tilted and Curved Surface Using Laser Focusing System

Laser focusing systems analyze the reflected laser beam from the specimen to return the defocus distance and direction, which also can be used for micro and sub-micro measurement. When curved or tilted surface is taken into account, this approach comes with inappropriateness because the reflected beam is deformed due to the differential incident angle of the incident beam. Employing image processing, we take further step to analyze the beam and manage to obtain both tilted angle and position of the specimen. A simulation model built on Zemax (Zemax LLC, Stansted, United Kingdom) works as theoretical model. The reflected beam is focused to a charge couple device (CCD) by a receiving lens. The focus pattern is then analyzed with the theoretical model. This technique returns high precision measurement results, including position, tilted angle and tilted direction of the tangent plane at the measured point.