A process for selective neutralization of H.sup.- ions in a magnetic field to produce an intense negative hydrogen ion beam with spin polarized protons, comprising the steps of:
- providing a multi-ampere beam of H.sup.- ions;
- providing a beam of laser light, any photon of which has sufficient energy to photodetach one electron from any one of the H.sup.- ions;
- providing a uniform solenoidal magnetic field around a portion of the length of said beam of H.sup.- ions to effectively spin polarize the H.sup.- ions in said beam, thereby to produce a first group of ions with proton spin aligned with said magnetic field and to produce a second group of ions with proton spin opposed to said magnetic field;
- directing said beam of laser light through the spin polarized beam of H.sup.- ions to selectively neutralize the majority of the ions in one of said groups, without neutralizing the ions in the other group;
- separating said one group of ions from said other group of ions, and directing said other group of ions in an intense H.sup.- ion beam toward a predetermined objective.