The electron spin in strong field tunnelionization

隧道穿过旋转势垒是有自旋选择性的。简而言之，这是巴思和斯米尔诺娃最近发表的一系列理论论文中令人惊讶的预测。本项目旨在对这一预测进行第一次实验检验。如今，基于泰坦蓝宝石的飞秒激光通常可以在800 nm的波长下达到1014 W/cm2或更高的强度(相当于每个光子1.5 eV的能量)。暴露在如此强的激光脉冲下的原子或分子可以通过场诱导隧穿有效地电离。对于圆偏振光，需要被电离电子克服的隧道势垒是旋转的。上述新颖的理论工作预言了在使用圆偏振激光脉冲的情况下，稀有气体原子通过强场隧道电离发射的电子的高度自旋极化。这一影响深远的预测仍需实验证实。因此，本实验方案的目标是进行一系列实验来详细检验这一理论。我们建议用强而短的圆偏振激光脉冲照射稀有气体原子，测量不同原子物种、不同强度和不同波长的电子发射电子的自旋偏振度。除了验证预测的效果外，还可以通过改变发射电子的波长、场强和结合能参数来检验其假设的潜在物理解释。申请者小组的准备工作已经进行，并产生了非常有希望的结果。如果成功，该项目将在第二个资助期扩展到分子和激光对准的分子。

Tunneling through a rotating barrier is spin selective. This is, in short, the surprising prediction of a series of recent theoretical papers by Barth and Smirnova. The present project aims at performing the first experimental test of that prediction. Nowadays, Titan Sapphire-based femtosecond-lasers allow to routinely reach intensities in the range of 1014 W/cm2 and higher at a wavelength of 800 nm (which is equivalent to an energy of 1.5 eV per photon). Atoms or molecules exposed to such a strong laser pulse are efficiently ionized by field induced tunneling. For circularly polarized light the tunnel barrier, that needs to be overcome by the ionized electron, is rotating. The above mentioned novel theoretical work predicts a high degree of spin polarization of electrons emitted by strong field tunnel ionization from rare gas atoms in case circularly polarized laser pulses are employed. This far reaching prediction still needs experimental confirmation. Therefore the goal of the present experimental proposal is to perform a series of experiments to test this theory in detail. We propose to shoot a strong and short circularly polarized laser pulse on rare gas atoms and measure the degree of spin polarization as function of the electron energy of the emitted electron for different atomic species, different intensities and different wavelengths. In addition to verifying the predicted effect its assumed underlying physical explanation can be tested by varying the parameters wavelength, field strength and binding energy of the emitted electron. Preparatory work by the group of the applicant has already been performed and yielded very promising results. If successful the project will be extended to molecules and also laser aligned molecules in a second funding period.