Optical Spectra and Gain Properties of Ho3＋/Pr3＋ Co-doped LiYF4 Crystal

• Published in: Journal of materials science & technology Vol. 30; no. 9; pp. 910 - 916
• Main Authors: Peng, Jiangtao, Xia, Haiping, Wang, Peiyuan, Hu, Haoyang, Tang, Lei, Zhang, Yuepin, Jiang, Haochuan, Chen, Baojiu
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2014
• Subjects: 2.9 μm; Gain cross section; Ho3/Pr3; Judd-Ofelt理论; LiYF4 crystal; LiYF4晶体; Optical spectra; 中红外激光器; 光学光谱; 共掺杂; 发射截面; 增益; 镨离子; Ho3/Pr3; 2.9 μm; Optical spectra; Gain cross section; LiYF4 crystal
• ISSN: 1005-0302; 1941-1162
• DOI: 10.1016/j.jmst.2013.09.014

The LiYF4 single crystals singly doped Ho3＋ and co-doped Ho3＋, Pr3＋ ions were grown by a modified Bridgman method. The Judd-Ofelt strength parameters （Ω2, Ω4, Ω6） of No3＋ were calculated according to the absorption spectra and the Judd-Ofelt theory, by which the radiative transition probabilities （A）, fluorescence branching ratios （β） and radiative lifetime （τ rad） were obtained. The radiative lifetimes of 5/6 and 5/7 levels in Ho3＋ （1 mol%）：LiYF4 are 10.89 and 20.19 ms, respectively, while 9.77 and 18.50 ms in Ho3＋/pr3＋ doped crystals. Hence, the τ rad of 5/7 level decreases significantly by introduction of Pr3＋ into Ho3＋：LiYF4 crystal which is beneficial to the emission of 2.9 μm. The maximum emission cross section of Ho3＋：LiYF4 crystal located at 2.05 μm calculated by McCumber theory is 0.51 ×10-20 cm2 which is compared with other crystals. The maximum emission cross section at 2948 nm in Ho3＋/pr3＋ co-doped LiYF4 crystal obtained by Fuchtbauer- Ladenburg theory is 0.68 × 10-20 cm2, and is larger than the value of 0.53 × 10-20 cm2 in Ho3＋ singly doped LiYF4 crystal. Based on the absorption and emission cross section spectra, the gain cross section spectra were calculated. In the Ho3- ions singly doped LiYF4 crystal, the gain cross sections for 2.05 μm infrared emission becomes positive once the population inversion level reaches 30%. It means that the pump threshold for obtaining 2.05 μm laser is probably lower which is an advantage for Ho3＋-doped LiYF4 2.05 μm infrared lasers. The calculated gain cross section for 2.9 μm mid-infrared emission does not become positive until the population inversion level reaches 40% in Ho3＋/pr3＋：LiYF4 crystal, but 50% in Ho3＋ singly doped LiYF4 crystal, indicating that a low pumping threshold is achieved for the H03＋：5/6 → 5/7 laser operation with the introduction of Pr3＋ ions. It was also demonstrated that Pr3＋ ion can deplete rapidly the lower laser Ho3＋：5/7 level and has influence on the Ho3＋：5/6 level. The Ho3＋/pr3＋：LiYF4 crystal may be a potential media for 2.9 μm mid-infrared laser.