Selection of Single Harmonic Emission Peak for Producing Isolated Attosecond Pulse via Chirped-UV Combined Field

Abstract

Abstract A potential method to produce isolated attosecond pulses (IAPs) by using low-intensity chirped-UV combined field has been investigated. The results can be separated into three parts. First, by properly introducing the mid-chirp or down-chirp of the low-intensity laser field, the harmonic cutoff can be extended and achieve the referenced value, which is produced from the high-intensity referenced field. Moreover, the spectral continuum is contributed by a single harmonic emission peak, which is beneficial to produce IAPs. However, the harmonic yield is very low due to the lower driven laser intensity. Second, by properly adding a UV pulse, the harmonic yield can be enhanced and achieve the referenced value due to the UV resonance ionisation. The intensity of the combined field is lower than that of the referenced field, which reduces the experimental requirements for producing high-intensity spectral continuum. Third, with the introduction of the positive or negative inhomogeneous effect of the mid-chirped combined field or down-chirped combined field, respectively, the similar harmonic cutoff and harmonic yield can also be obtained but with a much lower driven laser intensity. Finally, by superposing the harmonics on the spectral continuum, the IAPs with the durations of sub-38 as can be obtained.