1. M. N. Palatnikov, V. A. Sandler, N. V. Sidorov, et al., Fiz. Tverd. Tela (St. Petersburg) 42, 1456 (2000) [Phys. Solid State 42, 1499 (2000)].
2. A. A. Blistanov, Crystals in Quantum and Nonlinear Optics (Izd-vo MISIS, Moscow, 2000) [in Russian].
3. S. V. Evdokimov, R. I. Shostak, and A. V. Yatsenko, Fiz. Tverd. Tela (St. Petersburg) 49, 1866 (2007) [Phys. Solid State 49, 1957 (2007)].
4. I. Franke, E. Talik, K. Roleder, et al., J. Phys. D: Appl. Phys. 38, 4308 (2005).
5. S. R. Phillpot and V. Gopalan, Appl. Phys. Lett. 84, 1916 (2004).