Spin-polarized electrons produced by a sequence of two femtosecond pulses. Calculation of differential and global polarization rates

This paper presents a theoretical analysis of the possibilities of producing spin-polarized electrons with a sequence of two ultra-short time-delayed laser pulses. The first pulse, which is right circularly polarized, excites resonantly the fine structure np level of potassium atoms leading to a spin-flip and thus polarizing the atom. The second pulse ionizes the system thereby resulting in spin-polarized electron release. We examine and compare several situations corresponding to different polarizations of the ionizing pulse (sigma (+), sigma (-) and pi). For each case we derive analytical expressions;for the angular and global electron spin-polarization rates as well as for the differential cross sections. The obtained rates can be very high (up to 100%) and can be controlled accurately on the femtosecond time scale by varying the time delay between the pulses.