Xi'an Institute of Optics and Fine Mechanics has made new progress in the research of attosecond high spatiotemporal resolution imaging

The attosecond light source has the characteristics of ultra short pulse width, short wavelength, high coherence, and high-precision synchronous control, and has extremely high potential for application in the field of ultrafast imaging. Especially when the attosecond light source reaches the "water window" band, oxygen and hydrogen atoms have weak absorption of X-rays in this band, so water is relatively transparent to it, while basic elements such as carbon and nitrogen that make up living organisms have strong absorption of X-rays in this band. Therefore, high contrast imaging of biological samples can be achieved, which is expected to promote the research of high spatiotemporal resolution living cells. However, constrained by the uncertain relationship between time and energy, attosecond pulses have both extremely high time resolution and ultra wide spectra, which can cause significant color differences in imaging systems. For example, isolated attosecond pulses generated by high-order harmonics can have a pulse width of around 50 as and a typical bandwidth of over 100% (where Δ λ represents the full width of the spectrum and λ c represents the center wavelength).

Figure 1. Demonstration of multi-color diffraction. (a) Diffraction setting. (b) Example image. (c) FT of (b). (d) Obtained through zero padding around (b). (e) FT of (d). (f) Obtain (e) through cropping.

Meanwhile, attosecond pulses are typically in the extreme ultraviolet/soft X-ray wavelength range and lack high-quality optical components for reflection, focusing, beam splitting, and combining, which imposes many limitations on imaging systems. Therefore, in order to achieve attosecond imaging technology, it is necessary to overcome the difficulties of short wave band imaging and solve the interference between different spectral components in ultra wideband spectra, which is a major challenge that troubles current research at home and abroad.

Figure 2. (a) (d) Narrow band coherent diffraction imaging; (b) (e) Direct inversion results of broadband optical diffraction patterns; (c) (f) Broadband coherent diffraction imaging achieved by the monochromatization method proposed by the team

Recently, the Amis Science and Technology Research Center of Xi'an Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, made new progress in the research of high spatiotemporal resolution imaging in Amis. The research results were published in the international high-level academic journal Photonics Research (IF: 7.254). The first author of the paper is Li Boyang, Special Research Assistant of Xi'an Institute of Optics and Mechanics, Chinese Academy of Sciences, and the correspondence author is Wang Hushan, Associate Researcher and Fu Yuxi, Researcher.

The research team proposed an efficient gradient monochromatization method based on Fourier transform mode mapping, which can process complex/broad spectrum diffraction patterns to obtain high-quality monochromatic diffraction patterns, and then use traditional coherent diffraction imaging methods to achieve high-resolution imaging (as shown in Figure 2). This method greatly expands the applicable bandwidth of imaging light sources, supports the use of light sources with spectral bandwidth up to 140% for single shot imaging, and compresses the computation time to the second level. At the same time, this method also supports comb like spectra spanning multiple octave bands, enabling imaging applications of high-order harmonic light sources (attosecond pulse trains) with higher luminous flux. In addition, based on this diffraction imaging technology, the research team also proposed a spectral measurement method without gratings and lenses, which reduces the difficulty of measuring attosecond pulse spectra in the extreme ultraviolet/X-ray band. The research achievement has taken a crucial step towards breaking through the high spatiotemporal resolution imaging of attosecond, providing important technical support for the imaging terminal of "advanced attosecond laser facilities", and is expected to promote the application and development of attosecond light sources in laser precision processing, biomedicine, semiconductors and other fields.

The research work has been supported by the national key research and development plan - the special project of intergovernmental international scientific and technological innovation cooperation, the youth team plan of the Chinese Academy of Sciences in the field of stable support for basic research, the Chinese Academy of Sciences international partnership plan, the pre research of major scientific and technological infrastructure of the Chinese Academy of Sciences, the basic research plan of natural sciences in Shaanxi Province and other projects.

Source: Opticsky