rays by scattering the light energy or by absorbing the light energy or both that is the inclusions 30 may be of a type that scatters light energy without significant absorption or a type that absorbs light energy without significant scattering or may comprise both types types of inclusions that tend to scatter more than absorb light energy include reflective metal particles such as aluminum gold or similar metals or even transparent materials with refractive indexes different from the refractive index of the light propagating material 28 such as diamond zirconium oxide and like materials in addition inclusions that tend to scatter rather than absorb light energy may be grain boundaries of a polycrystalline material such as zinc selenide znse types of inclusions that tend to absorb rather than scatter light energy include particles of carbon or graphite iron oxide manganese dioxide and like materials either one or both types of inclusions may be present in light propagating material 28 as may be desired thus if a relatively low temperature high scatter probe is desired only inclusions that scatter rather than absorb light energy will be preferred where it is desired to have a probe that operates at a very high temperature only inclusions that absorb rather than scatter light energy will be preferred a preferred material for light propagating material 28 is a form of aluminum oxide sold under the trade name 34 lucalox 34 this material has a purity.