Abstract: A waveguide sensing element has a substrate having an input opening adapted to house an input optical fiber and an output opening adapted to house an output optical fiber. The input optical fiber transmits electromagnetic radiation, and the output optical fiber emits the electromagnetic radiation. The waveguide sensing element also has a guiding layer disposed adjacent the substrate. The guiding layer has a beveled end face. The angle of the bevel is chosen so that the guiding layer selects only those modes within a given range--i.e., high order modes. This increases the spectral absorption measurement sensitivity as compared to a waveguide sensing element which uses the complete mode spectrum. Such a highly sensitive waveguide sensing element has been found to be particularly useful as an internal reflection spectroscopic sensing element.