A hand held device having an optical fiber with a radiation emitter carried at a free end, the optical fiber being attached to a handle that includes a knob which allows movement of a flexible tubular sleeve from a position covering the fiber and emitter to a position exposing the emitter and a length of fiber adjacent to it, the sleeve also having a sharp metal cleat extending from its end, the cleat being an end of a length of wire which passes through a separate channel of the sleeve to the knob without being attached to the sleeve. An application of this device is for inserting the emitter into a mass of material in order to irradiate the material from within.