Patent ID: 7317194

Claim:
A method of spectrographic measurement, comprising: (a) generating light energy using an 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 excitation energy 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 a single one of said elements; (j) for each measurement signal associated with a single one of said elements of said multielement optical detector, mixing said measurement signal with its respective one of said heterodyne signals to generate a plurality of low-frequency measurement modulation products, one low-frequency measurement modulation product being associated with each of said modulation frequencies and comprising the difference between a single modulation frequency and its associated heterodyne frequency and having a measurement amplitude and phase; (k) mixing said reference excitation energy with its respective one of said heterodyne signals to generate a plurality of reference modulation products, one reference modulation product being associated with each of said modulation frequencies and comprising the difference between a single modulation frequency and its associated heterodyne frequency and having a reference amplitude and phase, each reference modulation product 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 low-frequency 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.