An apparatus for detecting one or more substances includes a radiation source emitting a beam of radiation and also includes a material capable of reflecting the beam of radiation with a first characteristic and capable of reflecting the beam of radiation with a second characteristic when the material interacts with the one or more substances. The apparatus also includes two or more radiation detectors to detect the first and second characteristics of the beam of radiation. A first one of the two or more radiation detectors is adjustably aligned to detect the first and second characteristics of the beam of radiation reflected from a first region of the material. A second one of the two or more radiation detectors is adjustably aligned to detect the first and second characteristics of the beam of radiation reflected from a second region of the material.