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REFERENCES: "D. Eimerl, L. Davis, S. Velsko, E. K. Graham and A. Zalkin. Optical, mechanical, and thermal properties of barium borate , <a href=\"https://doi.org/10.1063/1.339536\"><i>J. Appl. Phys.</i>, <b>62</b>, 1968-1983 (1987)</a>"
COMMENTS: "Beta barium borate (ß-BaB<sub>2</sub>O<sub>4</sub>, BBO). Extraordinary ray (e)."
DATA:
  - type: formula 4
    range: 0.22 1.06
    coefficients: 2.3730 0.0128 0 0.0156 1 0 0 0 1 -0.0044 2
