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Optical characterization of wavelength-shifting and scintillating-wavelength-shifting fibers

W. Bae, J. Cesar, K. Chen, J. Cho, D. Du, J. Edgar, L. Earthman, O. M. Falana, M. Gajda, C. Hurlbut, M. Jackson, K. Lang, C. Lee, J. Y. Lee, E. Liang, J. Liu, C. Maxwell, C. Murthy, D. Myers, S. Nguyen, T. O'Brien, M. Proga, T. Rodriguez, S. Syed, M. Zalikha, J. Zey

TL;DR

This work delivers a detailed optical characterization of new WLS and Sci-WLS fibers EJ-182I, EJ-160I, and EJ-160II, benchmarked against BCF-91A. By applying a double-exponential attenuation model, it demonstrates a clear wavelength dependence of attenuation, with the long attenuation length $\\Lambda_{ ext{long}}(\\lambda)$ increasing with wavelength and exhibiting dips at specific wavelengths. Immersion in water shows a pronounced reduction in light output and suppression of the short attenuation component due to decreased refractive-index contrast, highlighting environmental effects on fiber performance. The findings inform fiber choices and design considerations for LEGEND and similar experiments, and the authors plan to extend the study with more fiber variants and a ray-tracing Monte Carlo simulation to model photon transport in WLS and Sci-WLS fibers.

Abstract

We report results of optical characterizations of new wavelength-shifting and scintillating-wavelength-shifting fibers EJ-182 and EJ-160 from Eljen Technology and compare them to the wavelength-shifting fiber BCF-91A from Saint-Gobain. The wavelength-dependence of attenuation was derived from spectral measurements confirming that the long attenuation length increases with wavelength, while short attenuation effects become less significant at longer wavelengths. The impact of the environmental refractive index was studied by immersing the EJ-160II fiber in water. Immersing the fiber in water reduced the overall light output and suppressed the short attenuation component, which can be explained by reduced light-collection efficiency due to the smaller refractive-index contrast between the fiber cladding and the surrounding medium.

Optical characterization of wavelength-shifting and scintillating-wavelength-shifting fibers

TL;DR

This work delivers a detailed optical characterization of new WLS and Sci-WLS fibers EJ-182I, EJ-160I, and EJ-160II, benchmarked against BCF-91A. By applying a double-exponential attenuation model, it demonstrates a clear wavelength dependence of attenuation, with the long attenuation length increasing with wavelength and exhibiting dips at specific wavelengths. Immersion in water shows a pronounced reduction in light output and suppression of the short attenuation component due to decreased refractive-index contrast, highlighting environmental effects on fiber performance. The findings inform fiber choices and design considerations for LEGEND and similar experiments, and the authors plan to extend the study with more fiber variants and a ray-tracing Monte Carlo simulation to model photon transport in WLS and Sci-WLS fibers.

Abstract

We report results of optical characterizations of new wavelength-shifting and scintillating-wavelength-shifting fibers EJ-182 and EJ-160 from Eljen Technology and compare them to the wavelength-shifting fiber BCF-91A from Saint-Gobain. The wavelength-dependence of attenuation was derived from spectral measurements confirming that the long attenuation length increases with wavelength, while short attenuation effects become less significant at longer wavelengths. The impact of the environmental refractive index was studied by immersing the EJ-160II fiber in water. Immersing the fiber in water reduced the overall light output and suppressed the short attenuation component, which can be explained by reduced light-collection efficiency due to the smaller refractive-index contrast between the fiber cladding and the surrounding medium.

Paper Structure

This paper contains 9 sections, 3 equations, 13 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Fiber samples
  3. Measurement setup
  4. Optical characterization of fibers
  5. Emission spectra
  6. Attenuation lengths and light intensity
  7. Spectral attenuation lengths
  8. Measurements in water
  9. Conclusion

Figures (13)

  • Figure 1: Absorption (left) and emission (right) spectra of the WLS fibers (manufacturers' data). For reference, we include the emission spectra of tetraphenylbutadiene (TPB) from TPB-Leonhardt-JINST-2024, which is often used for shifting scintillation light of liquid argon or liquid xenon, and the quantum efficiency of Silicon Photomultiplier (SiPM) S13360 from Hamamatsu Photonics hamamatsu. All fibers and TPB spectra are normalized to their respective maxima.
  • Figure 2: Pictures of diamond fly-cut cross sections of the four tested fibers. These images were captured under a microscope with external illumination to highlight the core/cladding boundaries.
  • Figure 3: Photographs of the setup used in measurements. Left: a fiber arranged in a spiral groove. Right: A close-up view of the left picture.
  • Figure 4: LED emission spectrum, measured with our spectrophotometer. For reference, the emission spectrum of TPB TPB-Leonhardt-JINST-2024 and the quantum efficiency of a Hamamatsu SiPM S13360 hamamatsu are also shown.
  • Figure 5: Normalized emission spectra measured at 20 distances for the four tested fibers: BCF-91A (top left), EJ-182I (top right), EJ-160I (bottom left), and EJ-160II (bottom right).
  • ...and 8 more figures