Shanghai Institute Of Optics And Precision Machinery (SIPM) Makes Progress in Calibration Of Large-diameter Diffractive Lenses

Recently, the Joint Laboratory of High Power Laser Physics at the Shanghai Institute of Optics and Precision Machinery (SIPM) of the Chinese Academy of Sciences (CAS) proposed a single-exposure interferometric calibration method for large-caliber diffractive lenses, which provides a strong support for the engineering application of large-caliber diffractive lenses. The related research results were published in Optics Letters under the title Absolute measurement of focusing properties of a large-aperture diffractive lens.
Compared with folded-back focusing lenses, diffractive optical elements are flexible in design, large in aperture, light in weight, suitable for various wavelength bands, and capable of realizing complex optical functions, and photon sieves and ribbon sheets are typical examples of diffractive lenses. Considering that diffractive elements consist of a large number of microstructures, deviations are inevitable during processing, and thus the performance needs to be calibrated before use.
In this study, the natural background light of a large aperture diffractive lens is utilized as a reference, which enters the shear interferometric system together with the focused beam. The work is based on the interferogram recorded by the detector, the wavefront gradient of the focused beam with respect to the background light is obtained by Fourier analysis, then the transmitted wavefront is recovered using the mode method, and finally the focal length and focal spot morphology of the diffractive lens are numerically calculated.The experimental results of the 210-mm-aperture diffractive lens are in accordance with theoretical expectations. Ultra-large aperture waveband slices and photon sieves can be used in space interferometric telescopes. Beam-splitting photon sieves with self-supporting structures are suitable for focused imaging of EUV and soft x-rays. Multifocal photon sieves can be used for x-ray interferometric diagnosis of plasma.
This work was supported by the National Natural Science Foundation of China and the Strategic Pilot Program of the Chinese Academy of Sciences (Class A).

Figure 1. Measurement optical path of a large-diameter diffractive lens