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

Abstract

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 (σ + , σ − and π ).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.

Rabi oscillations of Morris-Shore–transformedN-state systems by elliptically polarized ultrafast laser pulses

“…We now turn our attention to the implication of the obtained results to possible applications towards polarization controls of electron or nuclear spins. Electron spin polarization controls by photo-excitation of atoms have been theoretically discussed for alkali atoms [31], where coherent excitations to nP states by circularlypolarized light was considered so that spin-orbit coupling exchanged spin and angular momenta. Alternatively, it can be considered, based on our demonstration, that the excited nP state is independently controlled to nP 1/2 and nP 3/2 through ultrafast Rabi oscillations.…”

Time-resolved 3D imaging of ultrafast spin–orbit wave packet dynamics

“…For instance, using polarization-tailored pump pulses allows to coherently control and image the time evolution of bound electron wave packets in atoms and molecules. Currently, we study the control of SOWPs in the perturbative regime by modulating the spectral phase and amplitude of the pump at the resonance frequencies (see equation (A.4)) as an initial step for the production of highly spinpolarized photoelectron wave packets [11,30,32,33]. In addition, extensions to the strong-field regime for efficient spin-selective production of photoelectrons are investigated.…”

“…Recently, the sub-femtosecond motion of SOWPs in krypton ions was observed using attosecond transient absorption spectroscopy [29]. In addition, coherent control of SOWPs based on shaped femtosecond laser pulses was demonstrated [28,[30][31][32] and the polarization dependence of SOWPs was studied experimentally [11,24] and proposed as a means to produce highly spin-polarized electrons [33,34]. So far, the dynamics of SOWPs have mainly been studied by means of scalar observables.…”

“…For example, in [11,25,35], oscillations in the ion yield from multiphotonionization of potassium atoms due to variation of the ionization probability during the SOWP time evolution were measured and analyzed in a bright-/dark-state formalism. However, since SO interaction induces a precession of the electron orbital alignment in angular direction [11,24,33], highly differential detection techniques are required to gain a complete spatiotemporal picture of the coupled angular momentum dynamics. In [26], photoelectron imaging spectroscopy was used to observe the angular dynamics of a SOWP in krypton atoms from linearly polarized excitation and ionization.…”

Ultrafast Nuclear Spin Polarization by Short Laser Pulses

“…Note that the similar schemes have been theoretically considered to polarize spin of photoelectrons [6,7,8] and photoions [7,8] using spin-orbit interactions, which has lead to the first experimental observation of ultrafast spin-polarization of Sr+ ions produced by fs laser pulses [9]. In contrast to the spin-orbit interaction, the hyperfine interaction is much weaker, and accordingly the hyperfine coupling time is even longer than the lifetime of the excited states.…”