Bi-layer attenuated total reflectance device providing optimized

Abstract

A sensing apparatus for spectral analysis in which the sensing head is bi-layered. The layer contacting the sample is formed of corrosion-resistant material, e.g., diamond. It is engaged by a supporting layer formed of infrared transparent material, e.g., zinc selenide through which radiation passes on its way to and from the sample-contacting layer. In order to avoid non-linearity in the sample absorbance results, incoming paraxial rays are all reflected in such a way that they are reflected at the same angle, and the same number of times, from the sample contacting surface of the corrosion resistant layer. The incoming rays may be reflected at a conical surface, or at a flat rooftop-like surface. The exiting rays are preferably reflected so that they are parallel to the incoming rays. Where a conical reflecting surface is used, it may be a surface of the zinc selenide layer, or a highly reflective surface provided by another element. In order to insure that each ray is reflected the same number of times at the sample, certain relationships are maintained between the width dimension of the return reflection surface (i.e., the reflection surface which causes rays to return to the sample after a previous reflection) and the thickness dimension between the return reflection surface and the sample.