the pump laser 39 s pulse train while the telescope 100 is set up in order to downsize the beam of the manipulated portion of the spectrum so it is equal to or slightly smaller than the original pump laser beam for mode matching the two beams entering the supercontinuum generator 50 once the now seeded output of the supercontinuum is formed it continues along the original path to form a ring which is output on the second arm of the beamsplitter 80 fig2 shows an embodiment of the component of the apparatus 11 consisting of elements 60 80 of 10 from fig1 which produces the spectrally narrow portion of the supercontinuum this diagram is not to be considered a 1 1 scaled ray tracing of the embodiment as some of the features have been enlarged for illustrative purposes in this embodiment the output of the supercontinuum generation process 50 is directed to the dispersive element 60 in this embodiment of the apparatus a diffraction grating 61 has been used however a prism or other dispersive element may also be used the a diffraction grating 61 is supported by a rotation stage 62 in such a way as the front face of the grating is directly over the rotational axis of the rotation stage such that the axis of rotation is orthogonal to the plane of the front face of the grating also important is.