Pulse duration dependence of harmonic yield of H 2 + and its isotopic molecule
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THE EUROPEAN PHYSICAL JOURNAL D
Regular Article
Pulse duration dependence of harmonic yield of H+ 2 and its isotopic molecule Cuiyan Xu1 , Liqiang Feng1 , Yan Qiao 2 , and Yi Li1,a 1 2
College of Science, Liaoning University of Technology, Jinzhou 121001, P.R. China Department of Pathophysiology, Basic Medical College of Zhengzhou University, Zhengzhou 450001, P.R. China Received 28 February 2020 / Received in final form 16 May 2020 Published online 1 July 2020 c EDP Sciences / Societ`
a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. 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 H2 is much + + higher than that of T2 . (ii) Driven by middle laser intensity, the optimal pulse durations for H2 and T+ 2 are + 15 cycles and 22 cycles, respectively. Moreover, the harmonic intensities of H+ 2 and T2 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 T2 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 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.
1 Introduction High-order harmonic generation (HHG) is an important frequency conversion process, where the high energy photons can be produced when atoms, molecules and solids driven by intense laser field [1–5]. The HHG process has been clearly declared by the semi-classical threestep model with the processes of ionization–acceleration– recombination [6]. In detail, when the laser field irradiated the atomic and molecular medium, the electrons in the bound state tunneled through the barrier; and then, the free electron moves in an oscillating electric field; finally, when the electric field is reversed, some of the ionized electrons return to the parent ion and recombine with the ground state to give off high-energy light with the cutoff energy of }ωmax = Ip +3.17Ekin , where Ip is the ionization potential and Ekin is the kinetic energy of an electron. Since the successful observation of HHG in experiments in the late 1980s [7], the study of HHG has been an important issue in strong field physics [8]. Because of the advantages of HHG, such as, frequency tunable and high coherence, the HHG spectra have many attractive applications, such as, the generation of isola
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