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

In this paper, the terahertz time-domain spectra of undoped and Er3+-doped YAG crystals with the components of Y3Al5O12, (Er0.2Y0.8)(3)Al5O12, and (Er0.5Y0.5)(3)Al5O12 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 2.10THz, whereas in the frequency region between 2.10 and 2.60THz, 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.