1. A method for spectrally analyzing an unknown sample for the existence of a characteristic, the method comprising the steps of: analyzing a first known sample having the characteristic and a second known sample not having the characteristic to identify less than fifty diagnostic spectral features of the characteristic, each diagnostic spectral feature being present at a different diagnostic wavelength in a mid-infrared spectral region; providing a spatially homogeneous region of the unknown sample that is substantially structurally homogenous so that the diagnostic spectral features have shifted less than 15 cm −1 than expected when directed at the spatially homogeneous region at each of the different diagnostic wavelengths; directing a plurality of interrogation beams at the unknown sample with a laser source, each of the interrogation beams being nominally monochromatic and having a different interrogation wavelength, and each interrogation wavelength corresponding to a different one of the diagnostic wavelengths; acquiring a plurality of separate output images of the unknown sample with an image sensor that senses light in the mid-infrared spectral region, wherein each of the output images is acquired while the unknown sample is illuminated by a different one of the interrogation beams; and analyzing less than fifty output images with a control system that includes a processor to determine whether the characteristic is present in the unknown sample.