Investigation of the elastic and photoelastic properties and refractive index of Tb<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">F</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Brillouin scattering of light from the acoustic phonons in Tb${\mathrm{F}}_{3}$ was investigated over a large temperature range. Values of the elastic and photoelastic coefficients and of Debye $\ensuremath{\Theta}=373$ K were calculated from data obtained at 300 K. The temperature dependence of scattering from the longitudinal phonons propagating along [010], [001], and [011] revealed an elastic anomaly of the lattice at about 180 K. In connection with these measurements the values and dispersions of the refractive indices were also measured.

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