Isolated attosecond pulse generation in the water window by tailored MIR femtosecond pulse laser

We numerically simulate the high-order harmonic generation in the frequency domain and attosecond pulse generation in the time domain from helium atom irradiated by a tailored MIR femtosecond pulse laser, which is synthesized by a 12 fs/1800 nm/2.71 x 10(14 )Wcm(-2) driving pulse laser and two gating pulse lasers including an 8 fs/1200 nm/1.62 x 10(14) Wcm(-2) and an 8 fs/800 nm/1.26 x 10(14) Wcm(-2). This combined pulse has the characteristics of a single-cycle mid-infrared femtosecond pulse with high intensity and stable carrier envelope phase, which current few-cycle MIR femtosecond pulse laser technology can't qualify. It is found that broadband supercontinuum harmonic spectra with regular plateau structure are generated, and the radiation efficiency of the harmonics is greatly improved compared with the case of a single pulse and two-color optimal synthesize pulses. After inverse Fourier transform, an isolated 66 as pulse with higher intensity can be obtained by superposing supercontinuum harmonics from the 70th to the 515th order. Here, the phase differences between three pulses have little effect on the numerical simulation results when they vary in the range of 0.37.

Automated summary

Through numerical simulation, it is found that using a tailored mid-infrared femtosecond pulse can generate broadband supercontinuum harmonic spectra in helium atom, and greatly improve the radiation efficiency of the harmonics. After inverse Fourier transform, an isolated attosecond pulse with higher intensity can be obtained. Additionally, the phase differences between the control pulses have little effect on the results.