Harmonic and attosecond pulse enhancement in the presence of noise

In this paper, we theoretically investigate the effect of noise on the photoionization, the generations of the high-order harmonic and the attosecond pulse irradiated from a model He⁺ ion. It shows that by properly adding the noise fields, such as the Gaussian white noise, the random light or the colour noise, both the ionization probabilities (IPs) and the harmonic yields can be enhanced by several orders of magnitude. Further, by tuning the noise intensity, a stochastic resonancelike curve is observed, showing the existence of an optimal noise in the ionization enhancement process. Finally, by superposing a properly selected harmonic, an intense attosecond pulse with a duration of 67 as is directly generated.