Measurement of High Numerical Aperture Spherical Wavefront Aberrations Using Quadriwave Lateral Shearing Interferometry (Invited)

Objective The quadriwave lateral shearing interferometer (QWLSI) offers advantages such as a compact structure, common-path interference, insensitivity to environmental vibration, and a wide detection range. The calibration of QWLSI’s aberration measurement system and parameters such as shear ratio relies on the precise measurement of the numerical aperture (NA) of the spherical wave. Therefore, in-situ calibration of the spherical wave NA under test must be achieved. Due to intrinsic limitations of the Zernike-based method, the Zernike aberration model fails to accurately capture tilt and defocus terms when reconstructing wavefronts. In order to achieve precise measurement of wavefront aberrations, measurements of tilt and defocus terms must be completed. QWLSI is capable of measuring wavefront aberrations of high-NA spherical waves, and this study aims to verify the performance of the proposed method and the QWLSI in this context. Methods A four-hole mask far-field spot method was proposed. This method replaces the grating in situ with a four-hole mask to obtain the centroid positions of the far-field spot, and employs the principle of similar triangles to measure the NA of the spherical wave under test. Additionally, this method simultaneously derives the three-dimensional coordinates of the center of the spherical wave relative to the center of the detector’s photosensitive surface, thereby enabling quantitative measurement of spherical wave tilt and defocus aberrations. This effectively expands the measurement capabilities of the QWLSI. Results and Discussions In simulations, the theoretical and measured values of the center coordinates and the NA of the spherical wave under test were compared. Simulations were performed for the QWLSI at spherical wave NA values of 0.4, 0.5, and 0.6. Simulation results demonstrate that the proposed four-hole mask far-field spot method exhibits high precision and robustness against environmental interference, and that QWLSI achieves high accuracy when measuring high-NA spherical waves. Multiple experimental measurements were conducted using a dial indicator and an autocollimator to systematically verify the measurement accuracy of NA, tilt, and defocus aberrations. Using QWLSI, wavefront measurements were performed on spherical waves with NA values of 0.4, 0.5, and 0.6, verifying that the wavefront measurement accuracy is within 0.0376λ RMS. Experimental results confirm high measurement accuracy for the spherical wave’s NA, tilt, and defocus aberrations, thus validating the correctness and feasibility of the proposed method. Furthermore, QWLSI exhibits high precision when measuring high-NA spherical waves. Conclusions The four-hole mask far-field spot method enables in-situ calibration of the NA for the QWLSI’s spherical wave under test, as well as measurement of tilt and defocus aberrations. Both simulation and experimental results demonstrate that this method exhibits high precision and robustness against environmental interference. Furthermore, the QWLSI achieves high-precision wavefront aberration measurement for spherical waves with NA≤ 0.6. Due to limitations of the current hardware setup, experimental verification of the method’s measurement accuracy for NA > 0.6 has not yet been completed. The next phase of work will focus on developing and optimizing the hardware platform to further improve the overall measurement accuracy and extend experimental validation of the method to higher NA regimes. This will further broaden the method’s potential applications in high-NA wavefront measurement and optical system calibration.