[en] Apparatus is described for neutralization of a beam of accelerated ions, such as hydrogen negative ions (H^-), using relatively efficient strip diode lasers which emit monochromatically at an appropriate wavelength (lambda = 8000 A for H^- ions) to strip the excess electrons by photodetachment. A cavity, formed by two or more reflectors spaced apart, causes the laser beams to undergo multiple reflections within the cavity, thus increasing the efficiency and reducing the illumination required to obtain an acceptable percentage (approx. 85%) of neutralization