areas of the filters 8 where no total reflection occurs of course this sensor may also be shielded against the sample by means of a cover layer 9 the sensor element shown in fig4 is a variant of that in fig3 in this case a wafer carrier layer 1 plus substrate 3 39 is used as a starting material which incorporates all the layers of a photodiode marked 3 39 in this figure from this wafer an annular photosensitive element 3 is etched out and the circular center area is filled up homogeneously with glass refractive index n 1 for instance by sputtering thus producing zone 20 which is transparent to the excitation radiation 11 this is then coated with a coupling layer 5 made of a colored glass filter material deposited by sputtering or of a plastic filter material applied by spinning with a refractive index n 2 in this case the coupling layer 5 is acting both as a lightguide for the radiation to be measured 12 and as a selective filter layer 8 which separates the fluorescent radiation from the reflected or scattered radiation from the filter layer 8 an opening 26 is etched out which is situated above the transparent zone 20 and which is then filled with glass that is transparent to the excitation radiation 11 finally the boundary layer 21 next to the.