Patent ID: 7582882

Claim:
A method of spectrographic measurement, comprising: (a) generating light energy using a solid state low capacitance excitation source, said light energy being caused to fall on a sample to be assayed, causing said sample to output an output optical signal; (b) generating a plurality of modulation frequencies; (c) generating a plurality of heterodyne frequencies to form a set of heterodyne signals at said heterodyne frequencies, each of said heterodyne frequencies being associated with one of said modulation frequencies; (d) coupling said modulation frequencies to said excitation source, causing said excitation source to generate excitation energy modulated in intensity in proportion to said modulation frequencies; (e) sampling a portion of said light energy generated using the solid state low capacitance excitation source to form a reference excitation signal; (f) focusing said output optical signal as an image modulated with said plurality of modulation frequencies on an image intensifier; (g) intensifying said image to form an intensified image modulated with said plurality of modulation frequencies; (h) receiving said intensified image modulated with said plurality of modulation frequencies on a multielement optical detector; (i) generating a plurality of measurement signals using said multielement optical detector, each measurement signal associated with one of said elements; (j) for each measurement signal associated with one of said elements of said multielement optical detector, said measurement signal being mixed with its respective one of said heterodyne signals to generate a plurality of low-frequency measurement modulation products, a low-frequency measurement modulation product being associated with each of said modulation frequencies and comprising the difference between a modulation frequency and its associated heterodyne frequency and having a measurement amplitude and phase; (k) mixing said reference excitation signal with said respective heterodyne signal to generate a plurality of reference modulation products, a reference modulation product being associated with each of said modulation frequencies and comprising the difference between a modulation frequency and its associated heterodyne frequency and having a reference amplitude and phase, each of said reference modulation products being associated with one of said measurement modulation products; and (l) for each of said plurality of low-frequency measurement modulation products, comparing said low-frequency measurement modulation product to its associated reference modulation product to generate an output signal indicating characteristics of said sample at the region on said sample associated with each of said elements.