Spectral imaging of a sample using a plurality of discrete mid-infrared wavelengths

A method for spectrally analyzing an unknown sample for the existence of a characteristic, the method comprising the steps of:

• analyzing a known sample having the characteristic to identify a plurality of diagnostic spectral features of the characteristic, each diagnostic spectral feature being present at a different diagnostic wavelength that is in a mid-infrared spectral region;
• preparing the unknown sample to have a spatially homogeneous region, the spatially homogeneous region 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 spatially homogeneous region 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.

A method for spectrally analyzing an unknown sample for the existence of a characteristic, the method comprising the steps of:

• spectrally analyzing a known sample having the characteristic with beams in a mid-infrared spectral range to identify a plurality of diagnostic spectral features of the characteristic based on absorbance values, each diagnostic spectral feature being present at a different diagnostic wavelength that is in a mid-infrared spectral region;
• preparing the unknown sample to have a spatially homogeneous region 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, the spatially homogeneous region not including density fluctuations and refractive index fluctuations;
• directing a plurality of interrogation beams at the spatially homogeneous region with a laser source, each of the interrogation beams 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.