Composite scanning and position decoupling method of confocal profilometer for measuring large aperture optical surfaces

Abstract Traditional confocal profilometers (CPs) obtain the axial response signal (ARS) through the axial scanning (AS) method and extract the peak value of the ARS to obtain the axial position information of the measured point. When measuring large diameter surfaces with point-by-point AS method, the horizontal motion platform needs to move step by step repeatedly, which seriously affects the measurement efficiency. In this paper, a new method of composite scanning (CS) and position decoupling for CPs is proposed to improve the measurement efficiency of large aperture optical surfaces. For the CS of the proposed method, the velocity of the horizontal motion platform is kept constant during the whole measurement process, while synchronously, the intensity curve of the composite axial response signal (CARS) including light intensity, axial position, and horizontal position information is recorded. The peak value of the detected CARS is extracted, and the relative axial and horizontal position information of the measured point is obtained simultaneously. Experimental results indicate that the measurement efficiency is increased by 10 times for a 100 mm diameter optical element measurement using the CS method.