Fig. 1. Energy level diagram of Ho：BYF

Fig. 2. Theoretical results of the outputted pulse energy versus the crystal length for different pump energy^［29］

Fig. 3. Cooling structures for (a) crystal-I；(b) crystal-II

Fig. 4. Theoretical results of the temperature variation of two crystals under the same pumping condition

Fig. 5. Simulated thermal stress of (a) crystal-I；(b) crystal-II under the same pumping conditions

Fig. 6. (a) Clamping diagram；(b) section diagram of the C-C' plane for crystal-I

Fig. 7. Schematic illustration of the experimental setup

Fig. 8. Photograph of our experimental system

Fig. 9. Relationship between the pump pulse width and the laser output energy（Repetition Rate = 2 Hz）

Fig. 10. Relationship between the drive current of pump LDs and the laser output energy（Repetition Rate = 2 Hz）

Fig. 11. Relationship between the pump light repetition rate and the laser output energy（Pulse Width = 90 μs）

Fig. 12. (a) Schematic of clamping diagram and (b) section diagram of the C-C' plane for crystal-II

Fig. 13. Relationship between the repetition rate and the laser output energy and power for both crystal-I and crystal-II（Pulse Width = 90 μs）