Recently, Zhang Junyong's team at the Joint Laboratory of High Power Laser Physics, Shanghai Institute of Optics and Precision Machinery (SIPM), Chinese Academy of Sciences (CAS), together with Prof. Yongpong Zhao's group at Harbin Institute of Technology (HIT), has made the first progress in the array control and shaping of EUV and soft x-ray focused optical fields, which has solved the problem of component limitation for diffractive imaging and interferometric sensing in the extreme ultraviolet (UV) and x-ray wavelength bands. The results were published as "Free light-shape focusing in extreme-ultraviolet radiation with self-evolutionary photon sieves" in Scientific Reports.
Since the discovery of x-rays by Roentgen, high-coherence short-wave light sources and high-performance short-wave focusing elements have been the two bottlenecks limiting the development of x-ray science. Synchrotron radiation and free-electron lasers, for example, focus on the soft and hard x-ray bands, while discharge plasma lasers cover the extreme ultraviolet and part of the soft x-ray band. As the problem of high-coherence short-wave light sources is alleviated, there is a more urgent need for focus modulation devices for EUV and x-rays. Whereas materials show strong absorption in the EUV and soft x-ray bands and strong penetration in the hard x-ray band, Fresnel waveband sheets are the only transmission focusing elements available at present. Shanghai Institute of Optical Machinery (SIOM) is the earlier unit in China to engage in the design and application of x-ray devices, especially on the basis of the traditional ribbon sheet and photon sieve, SIOM was the first to propose and develop a variety of multifocal photon sieves with different optical functions, such as the Grecian ladder photon sieve and the Fermat helix photon sieve, etc., which are able to meet the technical needs of short-wave diffraction imaging and interference sensing.
Compared with waveband slices with a limited number of rings, millions and billions of small apertures provide nearly unlimited design freedom for the emergence of functional photon sieves, and the joint team used optimization algorithms to design a self-evolving photon sieve, which achieves focused optical field array modulation and shaping in the EUV band. In the experiment, we optimized the 46.9nm laser from the discharge plasma laser 69.8nm, 46.9nm and 13.5nm to irradiate the photon sieve, recorded the focused light field with photoresist, and read the data from the atomic force microscope, and successfully obtained several sets of structured spots with 100nm focusing, and the results conformed to the theoretically calculated focusing in the diffraction limit.The realization of the modulation and shaping of EUV and x-ray arrays provides the opportunity for the structured lithography of short wave. and water window segments for in vivo biological cell imaging, interferometric diagnostics of laser plasma, x-ray microscopy and coherent diffraction imaging, etc. The realization of EUV and x-ray array modulation and shaping expands new development space.
This work was supported by the National Natural Science Foundation of China, the Shanghai Young Scientists Yangfan Program, and the Class A Strategic Pilot Project of the Chinese Academy of Sciences.
Fig. 1 Structural focusing of extreme ultraviolet (EUV) light, (a) AFM map of focal spot, (b-c) light intensity and phase of simulated focal spot
Fig. 2 Multilayer arrayed spot for extreme ultraviolet light
