Progress in Calibration of Large Aperture Diffractive Lenses in the High Power Laser Physics Joint Laboratory of Shanghai Institute of Optics and Mechanics

Recently, the High Power Laser Physics Joint Laboratory of Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, proposed a single exposure interferometric calibration method for large aperture diffractive lenses, which provides strong support for the engineering application of large aperture diffractive lenses. The relevant achievements are published in Optics Letters as "Absolute measurement of focusing properties of a large aperture diffractive lens".

Compared to reflective focusing lenses, diffractive optical elements are designed flexibly, have a large aperture, are lightweight, suitable for various wavebands, and can achieve complex optical functions. Photonic sieves and zone plates are typical representatives of diffractive lenses. Considering that diffraction elements are composed of a large number of microstructures, deviations are inevitable during the machining process, so performance calibration is necessary before use.

In this study, researchers used the natural background light of a large aperture diffractive lens as a reference and entered the shear interference system together with the focused beam. Based on the interference pattern recorded by the detector, the wavefront gradient of the focused beam relative to the background light is first obtained using Fourier analysis, and then the transmitted wavefront is reconstructed using the mode method. Finally, the focal length and focal spot morphology of the diffractive lens are numerically calculated. The experimental results of a 210mm aperture diffractive lens meet theoretical expectations. Ultra large aperture zone plates and photon sieves can be used for space interferometric telescopes. The self supporting beam splitting photon sieve is suitable for focusing imaging of EUV and soft X-ray. Multi focal photon sieves can be used for X-ray interference diagnosis of plasma.

This work was supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences' pilot A program.

Figure 1. Measurement Optical Path of Large Aperture Diffractive Lens

Figure 2. Experimental results of self-developed shear interferometer and measurement

Source: Shanghai Institute of Optics and Mechanics