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 H-2(+) and T-2(+) 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 H-2(+) is 20 cycles, and the harmonic intensity of H-2(+) is much higher than that of T-2(+). (ii) Driven by middle laser intensity, the optimal pulse durations for H-2(+) and T-2(+) are 15 cycles and 22 cycles, respectively. Moreover, the harmonic intensities of H-2(+) and T-2(+) from optimal pulse durations are almost the same. (iii) Driven by high laser intensity, the optimal pulse duration for T-2(+) is 15 cycles. For H-2(+), the enhancement of harmonic yield is very slow as pulse duration increases. Furthermore, the similar harmonic yields of H-2(+) and T-2(+) can be found before 12 cycles; while, when the pulse duration is larger than 12 cycles, the harmonic yield of H-2(+) is smaller than that of T-2(+). 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.