不同切割方向的Ho∶YAP晶体的激光输出特性存在差别。针对掺杂浓度为0.5%(原子数分数)的Ho∶YAP晶体开展a、b、c三种切割方向的激光输出特性实验研究。采用最大输出功率为44.3 W的1915 nm掺铥光纤激光器端面泵浦Ho∶YAP晶体,在三种切割方向上均获得了大于20 W的连续激光输出,其中b向切割晶体输出激光的中心波长近2118 nm,最大功率为23.6 W,斜率效率为61.98%,a向切割晶体与b向切割晶体的输出结果相近,c向切割晶体在达到最大输出功率时的中心波长为2129 nm;当采用腔内声光调Q获得脉冲输出时,a、c向切割晶体出现了中心波长偏移和多波长起振现象,而b向切割晶体则获得了中心波长近2118 nm的稳定脉冲输出,且其在重复频率为20 kHz时的最大平均输出功率为22.3 W,脉宽为20 ns,斜率效率为55.22%,光束质量因子分别为 Mx2=1.81和 My2=1.50。选用b向切割的Ho∶YAP晶体更有利于实现稳定且高效的2118 nm连续激光及纳秒级脉冲激光输出。

The laser output characteristics of Ho∶YAP crystal are discrepant along different cutting directions. In this study, a-cut, b-cut, and c-cut 0.5% (atomic fraction) Ho∶YAP crystals were used to investigate laser output characteristics. Using a thulium-doped fiber laser with a central wavelength of 1915 nm and maximum power of 44.3 W to end pump the Ho∶YAP crystal along each cutting direction, continuous-wave laser power greater than 20 W was achieved. For the b-cut crystal, the central wavelength of the output laser is close to 2118 nm and the maximum continuous-wave output power and slope efficiency are 23.6 W and 61.98%, respectively. The results for the a-cut crystal are similar to those for the b-cut crystal, but the central wavelength for the c-cut crystal is 2129 nm when the maximum output laser power is achieved. When the Ho∶YAP laser operates in an in-cavity acoustic-optical Q-switched state, central wavelength shifting and multi-wavelength resonance occur in the a-cut and c-cut crystals. However, for the b-cut crystal, a stable pulsed laser output with a central wavelength close to 2118 nm can be obtained. For a pulse repetition rate of 20 kHz, the maximum average output power, pulse width, slope efficiency, and beam quality factor are 22.3 W, 20 ns, 55.22%, Mx2=1.81, and My2=1.50, respectively. From these results, it can be concluded that the b-cut Ho∶YAP crystal is more suitable for obtaining stable and efficient 2118-nm continuous-wave lasers and nanosecond-level pulsed laser output.