High-intensity isolated attosecond X-ray pulse generation by using low-intensity ultraviolet-mid-infrared laser beam

An efficient approach to obtain the high-intensity isolated attosecond X-ray pulse has been proposed and studied by using the low-intensity ultraviolet-mid-infrared (UV-MIR) laser beam. It is found that with the superposition of the UV-MIR beam, not only the harmonic efficiency can be enhanced, but also the harmonic cutoff can be extended to the X-ray region. In detail, the results can be separated into two parts. Firstly, when the fundamental field is chosen to be the linearly polarization MIR field, the enhancement of the harmonic efficiency is sensitive to the pulse duration and the delay time of the UV pulse. Moreover, the enhancement of the harmonic spectrum is coming from the multiple harmonic emission peaks (HEPs). Secondly, when the fundamental field is chosen to be the polarization gating two circularly polarization MIR fields, the enhancement of the harmonic efficiency is independent on the pulse duration and the delay time of the UV pulse, which is much better for experimental realization. Moreover, the enhancement of the harmonic spectrum is nearly coming from the single HEP. Further, with the introduction of the unipolar pulse, the harmonic cutoff can be further extended and some sub-40 as single X-ray pulses with the intensity enhancement of 450 dB can be obtained