Abstract: A method and a device useful for identifying or detecting the presence of a material of interest, such as an explosive or a biological contaminant, in a sample is presented herein. The sample is illuminated with electromagnetic radiation at a predetermined set of wavelengths. An example of an illumination source includes a quantum cascade laser (QCL). The radiation reflects from a sample and is detected at pixels of a detector. Examples of the detectors include digital focal plane array (DFPA) cameras. Intensity of the reflected radiation is measured at each illumination wavelength. The pixels can be configured to add weighted intensities of the reflected radiation, the weights of the intensities being based on a predicted optical response value for the sample at the wavelengths of the first set and the second set of wavelengths. Based on the sum of weighted intensities of the reflected radiation, the likelihood that the material is present within the sample is determined.