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\bibitem{Nikoghosyan_etal2018} Nikoghosyan, A. S., Martirosyan, R. M., Hakhoumian, A. A., Makaryan, A. H., Tadevosyan, V. R., Goltsman, G. N., et al. (2018). Effect of absorption on the efficiency of THz radiation generation in a nonlinear crystal placed into a waveguide. \textit{Armenian J. Phys.}, \textit{11}(4), 257--262.

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