Source: National Natural Science Foundation of China 

Grant No: 11527807 

Project: Optical frequency comb in the extreme-ultraviolet(XUV)

Chief Specialist: Prof. Xiaojun Liu

Abstract: Optical frequency comb in the extreme ultraviolet (XUV comb) has been developed in the past ten years. As a newly invented tool, it represents an excellent combination of optical frequency comb technology and high harmonic generation (HHG) technique. Using the femtosecond enhancement cavity, the peak intensity of the driving comb is enhanced. With the benefit of harmonic generation of rare gas under high laser intensity, optical frequency comb in the extreme-ultraviolet can be achieved. XUV comb will cover the wavelength range that is required for the measurement of the transitions in H-like and He-like ions(e.g.,He+ and Li+ ions), and these measurements will provide a prominent test of the bound-state Quantum Electrodynamics (QED). In this proposal, we are going to build an XUV comb setup. Three parts, Near-IR driving comb system, XUV comb generation system and XUV comb detection system,are included in this setup. We particularly implement a new XUV output coupling scheme to use the generated XUV light more efficiently. We are also going to explore the possibility of using crystals as the working material, so that the XUV comb can cover more wavelength range. The shortest wavelength of this XUV comb setup is supposed to be 30 nm, and the power of the harmonic around 61 nm is above 30 μW. This high performance XUV comb can be applicable to the precision spectroscopy measurements in He+ and Li+ ions, aiming to the test of the bound-state QED theory.