Spectroscopic properties and laser performance of Nd3+ in lanthanum beryllate

Abstract

The neodymium‐doped lanthanum beryllate (La₂Be₂O₅ : Nd³⁺ or BEL : Nd) laser crystal is monoclinic, space group C_2h⁶‐C2/c. The fundamental vibration directions of light and the corresponding refractive indices have been determined as a function of wavelength. At 1 μm the indices are n_X=1.9641, n_Y=1.9974, and n_Z=2.0348. The energy levels of Nd³⁺ for the five lowest manifolds are presented. The low concentration limit for the Nd^{3+ 4}F_3/2 fluorescent lifetime in this crystal is 150 μsec and the two observed laser transitions have stimulated emission cross sections of 2.1×10⁻¹⁹ cm² for E∥X and 1.5×10⁻¹⁹ cm² for E∥Y. The laser wavelengths are 1.070 and 1.079 μm, respectively. In laser testing a higher slope efficiency was obtained in La₂Be₂O₅ : Nd than in Y₃Al₅O₁₂ : Nd (YAG : Nd). A Q‐switched output of 450 mJ from a 6.4‐mm‐diam by 76‐mm‐long X‐axis rod of BEL : Nd has been achieved for the 1.079‐μm transition, while a YAG : Nd rod of the same size in the same system yielded 160 mJ. The higher Q‐switched output in BEL : Nd is consistent with the lower stimulated emission cross sections as compared to that of YAG : Nd.