by locally selective doping of the quartz or glass material forming transparent plate 22 and makes it possible to arrange that all rays passing through the aperture are incident on the quartz air interface at near normal angles fig1 shows a further embodiment of a sensor 50 which uses an inverted winston cone 51 to reflect all the rays so that they are incident on the bottom surface 52 at less than the critical angle so there is no internal reflection and maximum transmission into the sensor 25 a winston cone is an off axis parabola of revolution designed to maximize collection of incoming rays within some field of view and is described further in winston r u201c light collection within the framework of geometric optics u201d j opt soc amer 60 245 247 1970 which document is hereby incorporated by reference in its entirety the winston cone 51 in this embodiment is a solid piece of quartz or glass preferably formed integrally with the transparent plate 22 and has a reflective coating on its side surfaces 53 in sensor 60 shown in fig1 the sensor 25 is mounted directly onto the back surface 22 a of the transparent plate 22 for this purpose a glue that is stable under the radiation to be detected and has a refractive.