Practical method for correcting heterochromatic stray light in dual‐channel spectrographs for colorimetry

Abstract

AbstractMeasurements by spectrophotometers more or less suffer from heterochromatic stray light generated in their spectrometers. It is divided into near‐band and off‐band stray lights. While the former appears near the spectral band of the incident flux, the latter distributes broadly across the whole range and is far more problematic from colorimetric point of view. This article presents a practical method for correcting off‐band stray light in dual‐channel array spectrographs often built in modern spectrophotometers. Unlike most correction methods using a line spread function, the presented method estimates the distribution of off‐band stray light across the array as the product of a device‐specific stray light distribution and a total stray light intensity. The latter depends on both the spectral power distribution of an incident flux and a device‐specific rate of change from the incident flux to the off‐band stray light. For further simplification, the method replaces wavelengths by several bands dividing the visible range owing to the moderate spectral dependence of the above rate of change. With those simplifications, the method is practical, effective, and robust enough to work in an inexpensive hand‐held spectrophotometer with the compact spectrograph which often suffers from off‐band stray light. The performance of the method was evaluated with two dual‐channel array spectrographs with and without 2nd‐order‐rejection filter. Specimen lights incident through ten different glass filters were measured and the errors caused by off‐band stray light in the pixel outputs from the array were successfully corrected by the method. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 431–439, 2017