Measuring profile of large hybrid aspherical diffractive infrared elements using confocal profilometer

The discrete profiles of large hybrid aspherical diffractive infrared elements (HADIEs) are measured using a confocal profilometer, and are extracted using a polynomial regression method. In this study, a HADIE with a diameter of 80 mm is measured using a confocal profilometer with maximum horizontal and vertical measurement ranges of 120 mm and 12 mm, respectively. The experimental results indicate that the confocal profilometer can compensate for the fabrication error of the HADIE, which can be reduced from 7.20 m to 1.05 m. Furthermore, a profile error of 0.64 m (measured peak-to-valley (P-V)) is obtained after correcting for the curvature error. The confocal profilometer is a nondestructive tool that can be used to measure the profile of HADIEs, and is particularly suitable in compensating for the fabrication error of fine optical elements.