Disordered crystals have become an important gain media in the field of ultrafast lasers due to their ultra-wide emission band. Recently, researchers from the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences have achieved new progress in studying disordered crystal materials. Relevant results were published in the Journal of Luminescence.

Laser crystals with the structure of ABCO₄(A=Ca, Sr, Ba, B=rare earth elements, C= Ga, Al or transition metal elements) are considered as one of the most potential ultrafast laser gain media due to the high structural disorder, good thermal property and low phonon energy to be used in the fields of medical treatment, industry and research. With the development of laser diode (LD) operating at 1.15 μm, the pump source of Ho³⁺:⁵I₆→⁵I₇ (3 μm) can be provided commercially. Therefore, studies of Ho³⁺ ions doped CaGdAlO₄ are of significance in the realization of mid-infrared ultrafast lasers pumped by commercial LD.

The research team reported the growth of Ho: CaGdAlO₄ crystal, analyzed the crystal quality, structure, segregation and polarized spectral property. The 3 μm transition (Ho³⁺:⁵I₆→⁵I₇) exhibits a wide luminescence band from 2,750 nm to 3,000 nm, which provides a theoretical foundation for the generation of mid-infrared ultrafast lasers. However, it faces a huge challenge due to the self-termination effect, arising from the fact that the fluorescence lifetime of ⁵I₆ energy level (0.22 ms) is considerably shorter than that of the ⁵I₇ energy level (8.64 ms), which is easy to cause the termination of mid-infrared emission. Hence, the research team grew and studied Ho³⁺ and Pr³⁺ co-doped CaGdAlO₄.

The research team found that Pr³⁺ plays an efficient deactivation effect with the deactivation efficiency of 96.2%. This work offered a novel potential laser medium for mid-infrared ultrafast lasers.

This work was supported by the National Natural Science Foundation of China, National Key R&D Program of China and Strategic Priority Research Program (B).

Fig.1 Mid-infrared emission spectra of Ho: CaGdAlO₄ and Ho, Pr: CaGdAlO₄ crystals. (Image by SIOM)

Fig. 2 Fluorescence decay curves of Ho: CaGdAlO₄ and Ho, Pr: CaGdAlO₄ crystals. (Image by SIOM)

Article website:
https://doi.org/10.1016/j.jlumin.2020.117620

Contact:
Mr. Wu Xiufeng
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS
Email: xfwu@siom.ac.cn