Abstract

In spectrophotometry and spectroradiometry photometric errors due to stray light passed by the monochromator employed are always present to some degree. The magnitude of the errors is dependent upon the spectral distribution of the energy entering the monochromator, the stray light characteristics of the monochromator, the effects of any filters or other components between the monochromator and the phototube, and the spectral response of the phototube or other receptor. Means are outlined of measuring the stray light characteristics of a monochromator and expressing the results in the form of a table or grid of numbers. From the grid values it is a relatively simple process to estimate closely the photometric errors in any given application. Finally, various means are suggested of reducing the effects of stray light errors.

© 1955 Optical Society of America

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  1. For a perfectly triangular shaped band pass the width of the base is twice the half-height width. However, most monochromators pass a more or less rounded triangle, and the question arises, where does the band-pass end and stray light begin? An arbitrary choice seems to be inevitable. This choice of limits of integration will often have a significant effect on the effective width of the bandpass as defined by A. C. Hardy and F. M. Young, J. Opt. Soc. Am. 39, 265 (1949).
    [Crossref]
  2. Essentially the same shape band pass results if monochromatic light of fixed wavelength enters the monochromator and the monochromator setting is varied, or if the setting remains fixed and the wavelength of the monochromatic light varies.

1949 (1)

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Figures (7)

Fig. 1
Fig. 1

Monochromator transmittance for wavelength setting λ′=0.

Fig. 2
Fig. 2

Optical system employed for measuring stray-light characteristics of a grating monochromator.

Fig. 3
Fig. 3

Phototube response as a function of the setting of a grating monochromator with a 546-millimicron energy entering.

Fig. 4
Fig. 4

A 436-millimicron light entering a monochromator.

Fig. 5
Fig. 5

A 644-millimicron light entering a monochromator.

Fig. 6
Fig. 6

Photomultiplier sensitivity as a function of applied voltage.

Fig. 7
Fig. 7

Sharp cut-off yellow filter on tungsten lamp. The circled points are predicted from stray light grid.

Tables (2)

Tables Icon

Table I K×104 (per millimicron).

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Table II K×104 (per millimicron).

Equations (13)

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R ( m ) = k 0 i ( λ ) t ( m , λ ) P ( λ ) d λ .
R o = k - i t o P d λ ,
R o = k - 1 1 i t o P d λ + k 1 3 i t o P d λ + .
R o = k - 1 1 i t o P d λ + k t o 2 P 2 1 3 i d λ + ,
R 2 = k P 2 1 3 i t 2 d λ .
1 3 R d λ = k P 2 A 2 1 3 i d λ ,
A 2 = 1 3 t 2 d λ .
R o = k - 1 1 i t o P d λ + t o 2 A 2 1 3 R d λ + ,
K o 2 = t o 2 / A 2 .
R o = - 1 1 i t o P d λ + K o 2 1 3 R d λ + .
R o = k t o 2 P 2 1 3 i d λ .
1 3 R d λ = k P 2 A 2 1 3 i d λ .
K o 2 = R o 1 3 R d λ .