apparatus for selective destruction or inactivation of cells is disclosed wherein cells are arrayed in a plane for successive illumination , by optical x - y scanning devices , with a first low powered light beam to produce in particular cells certain radiations responsive to the illumination . these response radiations are detected and used to enable a second higher powered light beam directed through substantially the same optical scanning paths , to destroy or inactivate the cells producing the response radiations . the illumination , response , detection , and high power radiation steps are accomplished by devices acting in times short as compared to the x - y scanning devices so as to make the accurate treatment of each of large numbers of cells highly effective . alternate embodiments disclose the use of a single laser light source to selectively provide both the low and high powered light beams , various x - y scanning arrangements , and various devices for correcting the spherical aberration of the scanned beams in variously positioned image planes .