High-order harmonic generation (HHG) results from a nonlinear response of atoms and molecules to intense laser fields. The emissions of HHG has the characteristics of short duration, broad bandwidth and tunable center wavelength, which has great applications in the micro ultrafast field with high resolutions. However, these potential applications are still limited by the spectral width, intensity and coherence of the harmonics.

By studying ultrafast electron dynamics inside the atom, the ultrafast optical team led by Professor Lu Peixiang presents a three-color method to generate efficient broadband water window supercontinuum. In our scheme, we adopt two control fields and the acceleration and ionization steps in the HHG process are simultaneously controlled, which can not only enhance the harmonic yields but also extend the harmonic cutoff to water window X-ray region. This supercontinuum can support the generation of intense isolated sub-100 as pulses with tunable central wavelengths, which has great significance in ultrafast detection and precision measurement fields.
Our research is published in Optics Express [Vol. 21, Issue 3, pp. 2683-2692 (2013)]. This work is supported by the National Natural Science Foundation of China under Grants No. 60925021, 11234004, 10904045 and the 973 Program of China under Grant No.2011CB808103.