Effect of isothermal annealing on the optical properties of Ca₃TaGa₃Si₂O₁₄ crystals

The effect of post-growth isothermal annealing in vacuum and in air on the optical properties of Ca₃TaGa₃Si₂O₁₄ crystal samples of Z and X-cuts has been studied. Spectral dependences of transmission coefficients were measured in the wavelength range (240–700) nm taking into account anisotropy and dichroism. On the Z-cut samples in the initial state an absorption band at λ = 360 nm in the ultraviolet range is observed, in the visible region – two absorption bands at λ = 460 nm and λ = 605 nm. Additionally, a band at λ = 290 nm was observed on the X-cut samples. When the sample was rotated around the direction of the light beam by 90 degrees, a change in the intensity of the absorption bands was observed. Annealing in vacuum leads to a decrease in the intensity of the absorption bands in the near ultraviolet and visible range, except for the absorption band at λ = 605 nm. Annealing in air leads to the opposite effect – an increase in the intensity of the absorption bands, except for the band λ = 605 nm. The value of the anomalous birefringence of the samples was estimated by the Mallard method. The degree of linear dichroism is calculated. It is shown that the degree of dichroism decreases as a result of annealing in vacuum, and increases during annealing in air.