The electron spin in strong field tunnelionization

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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.