A reflector/imaging optical element (11; 43) which is configured in order to transmit light (P1) of at least one first wavelength, concentrate light (P1) shone through the reflector/imaging optical element (11; 43) onto a first focal point (F) and reflect light (R) of at least one second wavelength, shone from the first focal point (F) onto the reflector/imaging optical element (11; 43), onto a second focal point (F′) of the reflector/imaging optical element (11; 43).