使用XUV阿秒脈衝與IR飛秒脈衝 使得D2+ 電子局部化解離的數值模擬

Abstract

阿秒雷射發明已經過了十年，時間分析光譜明顯是最重要的應用之一，另一種重要的應用是在控制原子分子過程裡。利用阿秒雷射會實現特殊的控制機制在Singh et al. 的實驗中，XUV阿秒脈衝列跟IR 飛秒脈衝相干照射於D2分子引起解離游離。 他們在TOF光譜裡發現一種不對稱(左右)，XUV脈衝游離D2分子產生D2+ 離子，接著IR脈衝輔助解離其D2+ 離子，不對稱產生的機制是來自於通過兩種路徑(2pσu ,1sσg)之間的干涉。 通過2pσu是吸收一個光子達到解離，1sσg是吸收三個光子再失去一個光子。 根據他們的研究，我們分析相同過程的細節，我們得到兩種結果，一個是發現新的路徑(1sσg沒有失得光子)是跟不對稱有關的機制；另一種結果是，使用較長的波長不對稱度大約會是Singh et al. 所得結果的十倍。

It has already been more than a decade since the first realization of attosecond laser pulse. One of the most attractive application of it is, obviously, time resolved spectroscopy. Another possible application application may be special types of control of atomic/molecular dynamics. Ultra-short perturbation can be expected to induce some unique dynamics. Singh et al. irradiated an XUV attosecond pulse train together with an IR femtosecond pulse coherently on D2 molecule, to induce dissociative ionization . The TOF spectrum of the fragment D+ ion shows left/right asymmetry. Here XUV pulse ionize D2 molecule, and the IR pulse assists the dissociation of the resultant D2+ ion. Asymmetry is attributed to the interference between the dissociation channel from the 2pσu state with one photon absorption and the one from the 1sσg state with three photon absorption and one photon emission. Following thier study, we analyzed the same process more in detail. Asymmetry oscillates as a function of the delay time between two laser pulses, and at specific values of delay asymmetry turns to zero. Even at this delay the kinetic energy resolved asymmetry shows asymmetry, and the zero delay is due to the cancellation of asymmetry in integrating it over kinetic energy. From the delay dependence of the kinetic energy resolved asymmetry indicates that the intereference is also attributed to the dissociation without photo absorbing/emission. We have also discussed how to enhance the asymmetry. By using a longer wavelength we have found that the asymmetry is increased by more than 10 times.