Abstract
Fluorescent optical fibers are used in nuclear detection and other forms of fiber-optic sensors. The trapping efficiency of a fluorescent optical fiber is defined by the optical energy trapped (or guided) by the fiber divided by the total energy emitted within it by the fluorescers that dope the fiber core. This characteristic is clearly important in determining the size of signals from these devices. A calculation of the trapping efficiency has been performed under the assumption that the fluorescence radiation is emitted isotropically by the individual fluorescers that are uniformly distributed throughout the core and are equally likely to be excited by particles or shorter-wavelength light. At the price of increased complexity, nothing in the analysis precludes the lifting of these restrictions. What is included in this analysis is the contribution of skew rays, which, to the author’s knowledge, is not presented elsewhere. A very simple expression for the trapping efficiency as a function of the cladding-to-core index ratio is derived. Also important in determining signal size is the transmission loss of the fluorescence radiation to either end of the fiber from the point of its generation. However, as it is a separate matter, it is not discussed here.
Highlights
Plastic fluorescent optical fibers have been widely discussed in detail as nuclear particle detectors as a result of the scintillation radiation they produce in their interior when bombarded with such particles
The fraction of the fluorescence power generated within the fiber that is trapped or guided by it is the subject of this paper
What is critical about skew rays in the context of trapping efficiency is the fact that their angle of incidence at the core-cladding interface depends on their azimuth, as well as their elevation (π∕2 − θ)
Summary
Plastic fluorescent optical fibers have been widely discussed in detail as nuclear particle detectors as a result of the scintillation radiation they produce in their interior when bombarded with such particles. Some of the light travels to either end of the fiber, where it generates an electrical signal in a photodetector. Four examples of such discussions are in Refs. 1–4, along with a textbook on radiation detection.[5] Fluorescent fibers are used in at least one optical sensor that is unrelated to particle detection.[6] In this case, the fluorescence at a given wavelength is generated by a pump light of a shorter wavelength operating continuously. The fraction of the fluorescence power generated within the fiber that is trapped or guided by it is the subject of this paper. The wavelength- and fluorescer-dependent loss of the signal during propagation will not be considered here, as it is a completely separate matter, measurements of transmission loss are presented in Refs. 3, 4, and 7
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