Pulse duration dependence of harmonic yield of H2+ and its isotopic molecule

We investigate the pulse duration dependence of harmonic yield in isotopic molecules of H2+ and T2+ driven by different laser intensities. Generally, the harmonic yield can be improved as pulse duration increases and then a maximum value can be obtained at the specific duration. Particularly, (i) driven by low laser intensity, the optimal pulse duration for H2+ is 20 cycles, and the harmonic intensity of H2+ is much higher than that of T2+. (ii) Driven by middle laser intensity, the optimal pulse durations for H2+ and T2+ are 15 cycles and 22 cycles, respectively. Moreover, the harmonic intensities of H2+ and T2+ from optimal pulse durations are almost the same. (iii) Driven by high laser intensity, the optimal pulse duration for T2+ is 15 cycles. For H2+, the enhancement of harmonic yield is very slow as pulse duration increases. Furthermore, the similar harmonic yields of H2+ and T2+ can be found before 12 cycles; while, when the pulse duration is larger than 12 cycles, the harmonic yield of H2+ is smaller than that of T2+. Taking advantage of harmonic yield changing law and with assistance of controlling pulse, the intense and broad spectral plateau can be obtained, which can support the generation of isolated attosecond pulses with durations of sub-40 as.