LD抽运复合YAG晶体温度场及热透镜效应研究

为了研究复合Nd:YAG激光晶体棒在端面抽运下的温度分布及热透镜效应,采用数值分析法得到了端面抽运激光晶体棒内温度场的数值解,当抽运光功率为18W、光斑半径0.2mm时,吸收系数为3.5/cm的复合晶体内最大温度为73.8℃;同时还得到了径向梯度折射率引起的轴向传播光相位延迟分布ΔΦt(r),并与相同条件下的普通晶体作了比较.结果表明,采用复合晶体可以大幅度降低激光晶体内的温升,并减小端面变形导致的透镜效应;复合晶体内的相位延迟分布ΔΦt(r)与普通晶体的相似,且不满足对半径r的二次方关系;热透镜和参考球面镜透镜的相位延迟分布之间存在畸变Δφ,在r较小(rp)时,相位延迟分布ΔΦt(r)可近似等效于一球面透镜,其等效焦距fGRIN值与普通晶体的接近,在r较大(r>wp)时,畸变Δφ随r增大而急剧增大.

An Investigation on temperature and thermal lens effects of laser diode end pumped composite YAG Rods

Temperature field and thermal lens effect of laser diode end pumped composite Nd∶ YAG rod were investigated through numerical analysis methods. Numerical solutions of temperature field were obtained. The maximum temperature was 73.8℃ for composite laser crystal with an absorption coefficient of 3.5/cm,under pump power of 18W with 0.2mm beam radius.And also phase-retardation distribution △Φt(r)of the axial transmission light caused by radial temperature gradients was obtained. Comparing with conventional rod,the results show that composite rod leads a lower temperature rise in laser rod,as well as reduces distortion of pump end which brings on lens effect of laser crystal. Phase-retardation distribution △Φt(r)in composite rod is similar to that of conventional laser rod,but it doesn't accord with radius quadratic relationship,there is an aberration △Φ between the phase retardation of the thermal lens and referenced spherical lens. △Φt(r)corresponds with that of a spherical lens approximately at r ＜wp,and the equivalent foci fGRIN approaches to the same value of conventional rod,whereas △Φ increases quickly with the increase of laser beam radius at r＞ wp.