Heat generation and thermal lensing in end-pumped Tm, Ho : YLF laser crystals

Thermal lensing in an end-pumped Tm,Ho: YLF laser crystal has been investigated with a theoretical model of continuous-wave quasi-three-level laser. Considering energy transfer upconversion (ETU) and ground-state reabsorption, the rate equations are given. The influence of ETU on the fractional thermal loading is calculated, and the results show that the latter critically depends on the pump-to-mode size ratio. The temperature distributions of a Tm,Ho : YLF crystal for different pump powers have been analysed. The output power and the focal length of the thermal lens as a function of pump power are obtained in experiment. The experimental results are compared with the theoretical results, and the experimental results show that the theoretical results are reasonable.