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首页> 外文会议>NATO advanced research workshop on super-intense laser-atom physics >INTENSE LASER-ATOM INTERACTIONS: BEYOND THE DIPOLE APPROXIMATION
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INTENSE LASER-ATOM INTERACTIONS: BEYOND THE DIPOLE APPROXIMATION

机译：激光激光器相互作用：超越偶极近似

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High harmonic generation by atoms and the stabilization of atoms are two intense-field phenomena that have been studied extensively in recent years. Harmonic generation can be understood qualitatively in terms of a semi-classical, three-step model. In this so-called simpleman's model", the active electron of the atom or ion is first detached by tunneling through an effective potential barrier formed by the instanta leous electric field of the laser pulse and the potential that binds the electron. The ejected electron is then assumed to move like a free particle in the electric field of the incident laser pulse. As the field reverses, the electron can re-collide with the core and recombine radiatively. A fully quantum mechanical description of harmonic generation that incorporates the essential ideas of the semi-classical model has been developed by Lewenstein and co-workers. Stabilization in the high-intensity, high-frequency regime can, on the other hand, be understood with the help of the high-frequency Floquet theory (HFFT) developed by Gavrila and co-workers. First, a transformation is made to the rest frame of a classical electron in the laser field. In this Kramers-Henneberger (K-H) frame, the electron experiences an effective time-dependent Coulomb potential that oscillates in space. Gavrila and co-workers have shown that in a stationary field, to first approximation, the dynamics of the atom in the field are governed by the time-average of this potential. This theory can be modified to accommodate the non-adiabatic evolution of the atom in a short laser pulse and, if the turn-on of the laser pulse is short enough, the electron wavepacket dynamics is essentially those of a free electron in the pulse. At high laser intensities, these relatively simple descriptions of harmonic generation and stabilization, respectively, can break down sinee non-dipole and relativistic effects must be accounted for. Indeed, for only moderately high intensities, the magnetic field component of the laser pulse cannot be a priori neglected. This magnetic field induces a drift in the laser propagation direction that, for a free classical electron, can be quite large. If taken literally, the semi-classical model of harmonic generation predicts no harmonic generation beyond the dipole approximation since an ejected electron would never return to the core. Similarly, in the high-frequency regime, a K-H transformation to the rest frame of an oscillating and drifting electron in a laser pulse would imply that the Coulomb potential moves away from the electron during the pulse. This, in turn, would affect the stabilization of the atom in the laser pulse. Obviously, these observations are oversimplified. However, we will show that the magnetic f eld component of an intense laser pulse can indeed strongly influence both high harmonic generation and stabilization.
机译：原子和原子稳定的高谐波产生是近年来广泛研究的两个激烈场现象。在半古典三步模型方面可以定性地理解谐波生成。在该所谓的SimpleMan的模型中，首先通过隧穿通过激光脉冲的瞬发的潜在电场和结合电子的电位隧穿形成的有效电位屏障来分离原子或离子的主动电子。喷射的电子是然后假设在入射激光脉冲的电场中类似于自由粒子。随着磁场反转，电子可以与核心辐射地重新碰撞。一个完全量子力学描述伴随的谐波产生Lewenstein和同事制定了半古典模型。另一方面，在高频浮子理论（HFFT）的帮助下，可以理解高强度，高频制度的稳定化，高强度，高频制度可以理解Gavrila和同事。首先，在激光场中的经典电子的静物框架上进行转换。在这个kramers-henneberger（kh）框架中，电子经历了效果在空间中振荡的IVE时间依赖的库仑电位。 Gavrila和同事已经表明，在一个固定的领域，首先近似，该领域中原子的动态受到这种潜力的时间平均值的管辖。该理论可以被修改以容纳在短的激光脉冲中原子的非绝热演变，并且如果激光脉冲的开启足够短，则电子波波基动态基本上是脉冲中的自由电子的动态。在高激光强度下，这些相对简单的谐波产生和稳定化的描述分别可以分解窦非偶极和相对论效应必须占。实际上，对于仅适度的高强度，激光脉冲的磁场分量不能是忽略的先验。该磁场引起激光传播方向的漂移，即用于自由经典电子，可以非常大。如果从字面上进行，谐波产生的半古典模型预测，由于喷射的电子永远不会返回到核心，因此不会超出偶极逼近的谐波产生。类似地，在高频状态下，在激光脉冲中的振荡和漂移电子的静止框架的K-H变换意味着库仑电位在脉冲期间远离电子移动。反过来，这将影响激光脉冲中原子的稳定性。显然，这些观察超薄了。然而，我们将表明，激光脉冲的磁性F ELD部件确实能够强烈影响高谐波产生和稳定化。

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