Terahertz optical parameters and lattice vibration-induced resonance of Er³⁺-doped Y₃Al₅O₁₂ crystal

Abstract

In this paper, the terahertz time-domain spectra of undoped and Er³⁺-doped YAG crystals with the components of Y₃Al₅O₁₂, (Er_0.2Y_0.8)₃Al₅O₁₂, and (Er_0.5Y_0.5)₃Al₅O₁₂ were detected and the corresponding frequency-domain spectra were also obtained after Fourier transform. It is shown that the three kinds of crystals are weakly dispersive and nearly transparent below 2.10 THz, whereas in the frequency region between 2.10 and 2.60 THz, dielectric resonance and obvious absorption are investigated which can be attributed to the low-frequency lattice phonon. It is also found that with the increase in Er³⁺ concentration, the resonant frequency exhibits a red shift and the values of refractive index show a small increase, which could be explained by the larger ionic mass and larger polarizability of Er³⁺ compared to Y³⁺, respectively. This work contributes to the research on YAG laser materials as well as novel materials applicable to THz devices.

Acknowledgments

This work was supported by the National Science Foundation of China under Grant Nos. 51032003, 11274198, and 51102148, and National High Technology Research and Development Program of China under Grant No. 2012AA030403.