We have developed a novel chemical detection technique based on IR micro-calorimetric spectroscopy that can be used to identify the presence of trace amounts of very low vapor pressure target compounds. Unlike numerous recently developed low-cost sensor approaches, the selectivity is derived from the unique differential temperature spectrum and does not require the questionable reliability of highly selective coatings to achieve the required specificity. This is accomplished by obtaining the IR micro-calorimetric absorption spectrum of a small number of molecules absorbed on the surface of a thermal detector after illumination through a scanning monochromator. We have obtained IR micro- calorimetric spectra for explosives such as TNT over the wavelength region 2.5 to 14.5 micrometers . Thus both sophisticated and relatively crude explosives compounds and components are detectable with this technique due to the recent development of ultra sensitive thermal-mechanical micro-structures. In addition to the above mentioned spectroscopy technique and associated data, the development of these advanced thermal detectors is also presented in detail.
The micro-sensor field is presently proliferating with designs and approaches. We have developed a micro-spectrometer for sensing applications containing five precision surfaces, including two off-axis aspheres. The entire monolith is less than six cubic centimeters in volume. This particular design contains a bandwidth of about 2 micrometers which is centered at 980 nm. Once an appropriate starting substrate was produced, the entire system was diamond turned to maintain the required surface figure, inter-surface spacing, and surface tilts. Only three diamond turned fixtures were needed to produce the monolith. The results proved to be more than adequate for many sensing applications. Slightly altered designs could easily be produced containing different bandwidths and resolutions as needed by the customer. Due to the spectrum of interest and the fabrication method, PMMA was the material chosen for this sensor. Other designs configurations incorporating BK7 and sapphire are presently being studied.
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