Generation of intense spectral continuum and isolated attosecond pulse by selecting single harmonic emission peak

Abstract

Generally, due to the interference of different harmonic emission peaks (HEPs), the intensity of high-order harmonic spectrum cannot keep enhancing as the pulse intensity increases. Thus, in this paper, a potential method to obtain an intense spectral continuum and isolated attosecond pulse (IAP) by selecting single HEP has been theoretically investigated. First, we choose the harmonic cutoff and the harmonic intensity from the optimal single-color laser intensity as the referenced values. Next, by properly choosing a lower-intensity negative chirped pulse, we see that the harmonic cutoff from this field is similar as that from the referenced field. Moreover, the spectral continuum is contributed by single HEP. However, the intensity of the spectral continuum from the negative chirped pulse is lower than that from the referenced field. As the pulse duration of the chirped pulse increases, the similar harmonic cutoff can also be found by using a much lower-intensity negative chirped pulse. However, the intensity of the spectral continuum is decreased compared with that from the shorter chirped pulse duration. Further, with the introduction of an IR or UV controlling pulse, the intensity of the spectral continuum can be enhanced up to the referenced value. Moreover, the longer the pulse duration of the controlling pulse is used, the lower the controlling pulse intensity is needed. Also, due to the UV resonance ionization, much lower UV intensity is needed to enhance the harmonic yield compared with that for adding IR controlling pulse case. All in all, the total laser intensity of the combined field (the fundamental pulse + the controlling pulse) is lower than that of the referenced field. Most importantly, the signal of the spectral continuum is only coming from single HEP, which can support the generations of intense IAPs with the durations of 30 as.