Spectrally analyzing an unknown sample (10A) includes (i) providing a spatially homogeneous region (10B) of the unknown sample (10A); (ii) directing a plurality of interrogation beams (16) at the spatially homogeneous region (10B) with a laser source (14), (iii) acquiring a separate output image (245) while the unknown sample (10A) is illuminated by each of the interrogation beams (16) with an image sensor (26A); and (iv) analyzing less than fifty output images (245) to analyze whether a characteristic is present in the unknown sample (10A) with a control system (28) that includes a processor. Each of the interrogation beams (16) is nominally monochromatic and has a different interrogation wavelength that is in the mid-infrared spectral range.