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Diode Array Spectral Correction

IP.com Disclosure Number: IPCOM000086923D
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 53K

Publishing Venue

IBM

Related People

Durham, OG: AUTHOR [+7]

Abstract

Self-scanning linear arrays of photodiodes are commercially available. The photodiodes operate in a charge storage mode wherein the output of each diode is proportional to exposure or to the light intensity times the time interval between successive scans. The longer the integration time for each diode, the greater its sensitivity or output. Such arrays find use in spectrophotometry wherein a polychromatic light beam is dispersed so as to illuminate the array whereby each element of the array represents a different wavelength. In such applications, the output response of the array varies across the spectral range. Described below are ways to provide a flat or uniform response across a spectral range by using a variable integration time for each element of the diode array.

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Diode Array Spectral Correction

Self-scanning linear arrays of photodiodes are commercially available. The photodiodes operate in a charge storage mode wherein the output of each diode is proportional to exposure or to the light intensity times the time interval between successive scans. The longer the integration time for each diode, the greater its sensitivity or output. Such arrays find use in spectrophotometry wherein a polychromatic light beam is dispersed so as to illuminate the array whereby each element of the array represents a different wavelength. In such applications, the output response of the array varies across the spectral range. Described below are ways to provide a flat or uniform response across a spectral range by using a variable integration time for each element of the diode array.

Shown in Fig. 2 is a system for obtaining the desired results in which an optical spectrometer 1 illuminates a diode array 2 across a wide band spectrum. A variable signal integrator 3 provides correction factors to the readings of the individual diodes of array 2 so as to produce a flat response. The correction factor would be obtained by calibrating the instrument against, for example, the reflectivity of a white standard which produces a series of uncorrected responses, as shown in Fig. 1. At each of the various wavelengths associated with the different diodes, the integration time would be proportional to the 4R or difference between the reflectivity of a given diode and the maximum reflectivity of any diode in the array.

In the system shown in Fig. 3, a shift-type storage register 4 is used to program a counter 5 that controls a gate 6 and the clocking pulse rate applied to array 2 from a clock 7. At the beginning of the cycle, a start pulse actuates or starts the running of clock 7 and, at the same time, gates the contents of the first position of register 4 into the counter. As the clock steps the counter down to zero, the counter 5 holds gate...