Coherent Emission from Rare Earth Ions in Electro-optic Crystals

Abstract

We report the observation of coherent emission from three rare‐earth ions in electro‐optic crystals. Oscillation is observed from Nd³⁺ ions in Bi₄Ge₃O₁₂, LiNbO₃, and Ba_0.75Ca_0.25Nb₂₆O at room temperature, and from Tm³⁺ and Ho³⁺ ions in LiNbO₃ at 77°K. Second‐harmonic radiation is obtained from LiNbO₃:Tm³⁺ and electric‐field modulation of threshold is observed for certain crystals of LiNbO₃:Nd³⁺. The latter effect is believed to arise from crystal strain. The propagation angle for phase‐matched second‐harmonic generation is calculated to lie at 43° to the c axis for both LiNbO₃:Tm³⁺ and LiNbO₃:Ho³⁺ at 77°K. Phasematched second‐harmonic generation from LiNbO₃:Nd³⁺ is not possible, since the maser line is an extraordinary wave. However, the polarization of the maser line in LiNbO₃:Nd³⁺ is appropriate for phasematched parametric frequency conversion in the near infrared. Attempts to observe such radiation were not successful due to the limited power available in the fundamental.