Abstract: A radioactively biased optical power limiter device is described which comprises first and second lenses disposed along an optical axis with a common focal plane therebetween, the first lens disposed for receiving electromagnetic energy input directed along the optical axis and focusing the input at the focal plane of the first and second lenses, a cell of optically nonlinear material disposed along the optical axis at the focal plane of the lenses, and a radioactive source of ionizing radiation disposed near or in the nonlinear material for selectively controlling the electromagnetic field level necessary to cause optical nonlinear effects in the cell.