Laser differential confocal axicon surface profile measurement method

Aiming to address the challenging problem of high-precision axicon profile measurement, a laser differential confocal axicon profile normal tracking (LDCNT) measurement method with high spatial resolution and anti-tilt capability is proposed in this paper. This method utilizes the principle of normal direction adaptive tracking for axicon profile measurements. It employs the Phase-Sensitive Detector (PSD) image plane spot position to calculate the normal angle and a high-precision rotary axis to drive the sensor normal to the measured surface to achieve the normal direction adaptive tracking measurement of the axicon profile and reduce the difficulty of pose adjustment of the measured axicon. Using the laser differential confocal focusing principle, the differential confocal signal is normalized to improve the axial resolution and avoid the Abbe error generated by the local inclination of the surface, thus realizing high-resolution and anti-tilt measurement of the axicon profile. Through the reference frame error decoupling axicon profile measurement and evaluation technique, spatial error compensation, three-dimensional profile reconstruction, and evaluation of the measurement data are performed to reduce the systematic measurement error and realize high-precision measurement and reconstruction of the axicon profile. Finally, the feasibility of the method is verified by measuring the profile of a standard cylinder and axicon at different axicon angles. The experimental analyses show that this method provides a new method for high-precision measurement of the axicon profile with Peak-to-Valley (PV) repeatability better than 40 nm (3σ) and Root-Mean-Square (RMS) repeatability better than 15 nm (3σ).