Investigation on temperature and thermal lens effects of laser diode end pumped quadrate composite YAG crystal

Temperature field and thermal lens effects of laser diode end pumped quadrate composite Nd:YAG rod are investigated through numerical analysis methods. Numerical solution of temperature field for end pumped configuration is obtained, as well as phase-retardation distribution ΔΦ_T(r) for the axial light caused by radial temperature gradient, and the results are compared with conventional crystal under the same pump condition. The results show that in both composite and conventional crystal, the differences of their highest temperature increase as the absorption coefficient increasing. Composite crystal leads a lower temperature rise in laser crystal, and also reduces the portion lens effect from the lessened distortion of pump end. ΔΦ_T(r) in composite crystal is similar to that of conventional one, and it does not accord with radius quadratic relationship. There is an aberration Δφ between the phase retardation of the thermal lens and referenced spherical lens. ΔΦ_T(r) corresponds with that of a spherical lens approximately at r<w_p, and the equivalent foci f_GRIN approaches to the same value of conventional rod, whereas Δφ increased quickly with the increase of laser beam radius at r>w_p.