We study the double ionization of atoms subjected to circularly polarized (CP) laser pulses. We analyze two fundamental ionization processes: the sequential (SDI) and nonsequential (NSDI) double ionization in the light of the rotating frame (RF) which naturally embeds nonadiabatic effects in CP pulses. We use and compare two adiabatic approximations: The adiabatic approximation in the laboratory frame (LF) and the adiabatic approximation in the RF. The adiabatic approximation in the RF encapsulates the energy variations of the electrons on subcycle timescales happening in the LF and this, by fully taking into account the ion-electron interaction. This allows us to identify two nonadiabatic effects including the lowering of the threshold intensity at which over-the-barrier ionization happens and the lowering of the ionization time of the electrons. As a consequence, these nonadiabatic effects facilitate over-the-barrier ionization and recollision-induced ionizations. We analyze the outcomes of these nonadiabatic effects on the recollision mechanism. We show that the laser envelope plays an instrumental role in a recollision channel in CP pulses at the heart of NSDI.

中文翻译：

---

圆偏振激光脉冲驱动的原子双电离的非绝热效应

我们研究了经受圆偏振（CP）激光脉冲的原子的双重电离。我们根据旋转框架（RF）分析了两个基本电离过程：顺序（SDI）和非顺序（NSDI）双重电离，这自然地将非绝热效应嵌入CP脉冲中。我们使用并比较了两种绝热近似：实验室框架（LF）中的绝热近似和RF中的绝热近似。RF中的绝热近似封装了LF中发生的子周期时标上电子的能量变化，并充分考虑了离子与电子之间的相互作用。这使我们能够确定两种非绝热效应，包括降低发生过势垒电离的阈值强度和降低电子的电离时间。结果，这些非绝热效应促进了越过屏障的电离和再碰撞诱导的电离。我们分析了这些非绝热效应对碰撞机理的影响。我们表明，激光包络在NSDI心脏的CP脉冲中的碰撞通道中发挥了重要作用。