that the radiation p 2 can be coupled into the waveguide 110 the influence of the sleeve 120 on the coupling efficiency will be explained below in further detail with reference to fig4 6 fig4 shows a curve ra that visualizes the angle u03c6 of the emitted radiation versus location with respect to the plane of the emitting surface 60 in an exemplary fashion it is assumed that the diameter of the emitting surface 60 is 2 mm and that the maximum radiation angle is 65 u00b0 1 1 rad fig4 shows that the radiation angle u03c6 varies over the location the radiation angle u03c6 reaches its maximum in the center area location 0 mm of the emitting surface 60 and approaches zero at both edges of the emitting surface 60 location u00b1 1 mm in fig5 the curve ra visualizes the radiation angle u03c6 of the radiation versus the location in the plane of the proximal end 130 of the waveguide 110 see fig1 it can be seen that the curve ra has changed its shape compared with fig4 and that the radiation angle u03c6 is larger than in fig4 in fig5 it is assumed in an exemplary fashion that the distance between the proximal end 130 of.