Large-aperture optical elements are widely used in a variety of optical systems, such as astronomical telescopes and inertial confinement fusion laser devices. To reduce the laser damage to the devices, it is usually necessary to increase the aperture of the optical elements to reduce the energy density. Although real-time on-line dynamic detection of large-aperture optical components has great significance, a large aperture under test is in contradiction with the small target surface of the detector. Therefore, the large-aperture wavefront must be reduced to match the detector size. Among the current wavefront sensors, radial-shearing interferometry can convert a large beam into a small diameter beam to fit the measurement instruments in a diagnostic system. In present study, we report a novel type of single-shot radial-shearing interferometry with an ultra-large aperture ancient Greek-ladder membrane photon sieve (aGPS). This method has the advantages of common path, strong stability, and high accuracy, and meets the requirement of large-aperture wavefront sensing. The proposed approach can be helpful for wavefront measurements of meter-scale optical elements and 10-m space telescopes.

Single-shot radial-shearing interferometry with an ultra-large aperture aGPS is proposed for the first time. The ancient Greek-ladder sequences are first encoded and then mapped into the photon sieves to generate an aGPS, which has the optical function of multiple foci in space. The 114 mm diameter aGPS with 150 million holes is designed and machined to carry out radial-shearing interferometry. In the experiment, the reason of low-contrast interferogram at different positions is analyzed, indicating the direction for later research. Furthermore, to improve the signal-to-noise ratio of the interferogram, the optical software GLAD is used to simulate the radial-shearing interferometry with sphere-wave illumination. Finally, based on the above analysis, non-confocal radial-shearing interferometric experiments with the aGPS are carried out to verify our proposed method.

Taking into account the difficult manufacture of a large-aperture membrane aGPS, two non-confocal mono-focal photon sieves are used to construct the radial-shearing interferometric path. Before properly starting the experiment, the two photon sieves are adjusted and placed in confocal condition. Then, the short focal-length photon sieve can move forward or backward from the confocal spots, and its transmission function is equivalent to that of an aGPS (Fig.2). The large-aperture radial-shearing interferometric path with an aGPS is shown in Fig. 3. The entire interference wavefront detection system consists of only one bifocal aGPS. Overall, compared with the mono-focal Fresnel zone plate, the aGPS has complex optical functions, which is conducive to the improvement and optimization of the interference path. The designed aGPS has a self-supporting structure, and it enables the processing and production of ultra-large aperture membrane photon sieves and does not introduce background aberrations (Fig.6). In addition, that only one aGPS realizes the radial-shearing interference optical path, breaks through the limitation of the aperture, and provides a new option for a large-aperture and high-precision wavefront sensing method. The experimental results exhibited in Figs. 7 and 8 show that photon sieves can be used for radial-shearing interferometry, and the wavefront measurement result of window glass with non-confocal photon sieves is consistent with that of the two traditional Fresnel zone plates.

This study demonstrates that the method of single-shot radial-shearing interferometry with an ultra-large aperture aGPS is effective. The aGPS not only has functions of axial splitting to realize radial-shearing interferometry with variable shear ratio but also can be fabricated with large aperture and does not introduce system aberration. Different from confocal radial-shearing interferometry, the non-focal radial-shearing interferogram is modulated by the spherical wave that can magnify the interference effect of the small-aberration wavefront. Our proposed method is verified by the optical experiment and provides a new way to measure the wavefront distributions of meter-scale optical elements and 10-m space telescopes.