Measurement of dual-component attenuation length in square BCF-92 and round Y11 wavelength-shifting fibers

Abstract Wavelength-Shifting (WLS) fibers convert ultraviolet and blue scintillation light into green wavelengths, enabling efficient light collection in particle physics detectors. By reducing sensitivity to background noise, these fibers improve signal quality and detection accuracy. A key parameter affecting their performance is the attenuation length, defined as the distance over which the transmitted light intensity decreases by a factor of 1/e. We report measurements of the dual-component attenuation length of square double-clad BCF-92 fibers (Saint-Gobain) and round Y11 fibers (Kuraray). Light transmission was studied using a pulsed source, and the attenuation profile was fitted with a double-exponential model to extract short- and long-component parameters. Two independent methods, namely using a spectrophotometer and using a PMT readout, were applied, yielding consistent results. Systematic tests performed under varying fiber and environmental conditions showed no significant variations, demonstrating the robustness and reproducibility of the measurements. The experimental setups, data-analysis methods, and implications for scintillation-detector design are presented and discussed.