We derive the analytical formula of the ratio of the ionization rates of degenerate valence ${\ensuremath{\pi}}_{\ifmmode\pm\else\textpm\fi{}}$ orbitals of prealigned linear molecules in strong circularly polarized (CP) laser fields. Interestingly, our theory shows that the ionization ratio for molecular orbitals with opposite azimuthal quantum numbers $\ifmmode\pm\else\textpm\fi{}|m|$ (e.g., ${\ensuremath{\pi}}_{\ifmmode\pm\else\textpm\fi{}}$) is identical to that for atomic orbitals with the same $\ifmmode\pm\else\textpm\fi{}|m|$ (e.g., ${p}_{\ifmmode\pm\else\textpm\fi{}}$). In general, the electron counter-rotating to the CP laser field tunnels more easily, not only for atoms but also for linear molecules. Our theoretical predictions are then verified by numerically solving the three-dimensional time-dependent Schr\"odinger equation for the ionization of the prealigned nitric oxide (NO) molecule in strong CP laser fields. Due to the spin-orbital coupling in the electronic ground state of NO and the sensitivity of ionization to the sense of electron rotation, the ionization of NO in CP fields can produce spin-polarized photoelectrons with high controllability of spin polarization up to
100.
Momentum-resolved scattering experiments with laser-cooled atomic targets have been performed since almost two decades with magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) setups. Compared to experiments with gas-jet targets, MOTRIMS features significantly lower target temperatures allowing for an excellent recoil ion momentum resolution. However, the coincident and momentum-resolved detection of electrons was long rendered impossible due to incompatible magnetic field requirements. Here we report on an experimental approach which is based on an all-optical
6Li atom trap that---in contrast to magneto-optical traps---does not require magnetic field gradients in the trapping region. Atom temperatures of about 2 mK and number densities up to
109 ${\mathrm{cm}}^{\ensuremath{-}3}$ make this trap ideally suited for momentum-resolved electron-ion coincidence experiments. The overall configuration of the trap is very similar to conventional magneto-optical traps. It mainly requires small modifications of laser beam geometries and polarization which makes it easily implementable in other existing MOTRIMS experiments.