Planck Spectrometer

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#The present invention relates to optical spectrometers and in particular to an optical spectrometer that may derive spectral characteristics of an object or material using generated thermal radiation emitted at a variety of temperatures.

#FIG. 1 is a block diagram of a first embodiment of the present invention employing a computer-controlled heated stage holding an object or material which thermally emits light toward one or more broadband detectors to provide a spectrum or spectral image of the object or material;

#FIG. 2 is a diagram depicting emissivity curves for different representative objects, Planck distributions of thermal radiation at different temperatures and power curves being the product of the emissivity curves, and the Planck distributions that can be used to derive the emissivity curves;

#FIG. 3 is a block diagram of the steps of a program executed by the computer of FIG. 1 to provide spectral measurements; and

#Referring now to FIG. 1, a spectrometer 10 of the present invention may provide a stage 12 supporting, and in thermal contact with, an emission source 14 whose spectral properties may be characterized. In one embodiment, the stage 12 may include an internal heater 16, for example, a resistive heating element, electrically communicating with a computer-controlled current source 18 such as an amplifier or controllable power supply. A temperature sensor 20 is in thermal communication with the emission source 14 via the stagel2 to monitor a temperature 22 of the emission source 14 during operation.

#An optical assembly 24 collects light 26 from thermal radiation generated by the emission source 14 to focus the same at a focal plane 30 on an array 32 of broadband detector elements 34. In one embodiment, the optical assembly 24 desirably functions in a mid-infrared range being generally understood to be 2-20 μm and may consist of one or more lenses, mirrors, zone plates and the like to provide the necessary focusing.

#The array 32 of broadband detector elements 34 desirably is a two-dimensional array suitable for imaging where each detector element 34 makes a power measurement that can produce a pixel in an image, for example, of the surface of the emission source 14. Each of the detector elements 34 may be identical providing an operating sensitivity to light having a wavelength anywhere between 3 and 13 μm and are not relied upon, alone, for frequency discrimination. Desirably the detector elements 34 have a sensitivity that is at least 90% of a peak sensitivity spanning at least 6 μm to 10 μm. Example such detector arrays 32 suitable for use with the present invention are commercially available from FLIR Systems Inc. having offices in Wilsonville Oregon under the trade name of Neutrino LC providing a resolution of 640×512 pixels in the midrange infrared region.