补偿走离角时产生的相位失配及其补偿方法
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摘要
在非线性频率变换中,常用级联晶体补偿走离角。然而在KTiOPO4晶体级联倍频实验中发现,当其中一块晶体沿通光轴旋转180°时,倍频转换效率急剧降低。理论分析表明,当一块晶体旋转180°后,其有效非线性系数正负号发生改变,等效于在级联晶体之间产生了大小为π的相位失配量,使倍频转换效率降低。提出了利用空气色散补偿该相位失配量的方法,相较于使用波片的相位失配量补偿方法,具有结构简单、温度稳定性好、无插入损耗和成本低等特点。实验结果表明,利用空气色散可以补偿相位失配量,消除单块晶体旋转对晶体级联倍频效率的影响,验证了理论分析的正确性以及空气色散补偿方法的可行性。
Crystal cascading is widely used for the compensation of walk-off angles in the nonlinear optical frequency conversion process.However,it is discovered that the conversion efficiency dramatically decreases when one of the cascaded crystals is rotated by 180° along the optical axis in the second harmonic generation experiment based on KTiOPO_4 crystal cascading.The theoretical analysis indicates that the crystal rotation of 180° changes the sign of the effective nonlinear coefficient,which is equivalent to the generation of a phase mismatch ofπand thus the second harmonic generation conversion efficiency decreases.A method based on air dispersion is proposed for the compensation of phase mismatch,which is characterized by simple configuration,solid temperature stability,low insert loss and low cost if compared with those for the compensation method based on wave plates.The experimental results show that the phase mismatch is compensated by air dispersion and the influence of crystal rotation on second harmonic generation conversion efficiency is eliminated.The validity of the theoretical analysis and the feasibility of the compensation method based on air dispersion are demonstrated.
Crystal cascading is widely used for the compensation of walk-off angles in the nonlinear optical frequency conversion process.However,it is discovered that the conversion efficiency dramatically decreases when one of the cascaded crystals is rotated by 180° along the optical axis in the second harmonic generation experiment based on KTiOPO_4 crystal cascading.The theoretical analysis indicates that the crystal rotation of 180° changes the sign of the effective nonlinear coefficient,which is equivalent to the generation of a phase mismatch ofπand thus the second harmonic generation conversion efficiency decreases.A method based on air dispersion is proposed for the compensation of phase mismatch,which is characterized by simple configuration,solid temperature stability,low insert loss and low cost if compared with those for the compensation method based on wave plates.The experimental results show that the phase mismatch is compensated by air dispersion and the influence of crystal rotation on second harmonic generation conversion efficiency is eliminated.The validity of the theoretical analysis and the feasibility of the compensation method based on air dispersion are demonstrated.
引文
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[2]Chaitanya Kumar S,Samanta G K,Devi K,et al.High-efficiency,multicrystal,single-pass,continuous-wave second harmonic generation[J].Optics Express,2011,19(12):11152-11169.
[3]Schulz W,Poprawe R.Manufacturing with novel high-power diode lasers[J].IEEE Journal of Selected Topics in Quantum Electronics,2000,6(4):696-705.
[4]Wen X,Han Y S,He J,et al.Generation of397.5nm ultra-violet laser by frequency doubling in a PPKTP-crystal semi-monolithic resonant cavity[J].Acta Optica Sinica,2016,36(4):0414001.温馨,韩亚帅,何军,等.PPKTP晶体半整体谐振腔倍频的397.5nm紫外激光输出[J].光学学报,2016,36(4):0414001.
[5]Zhang Y T,Qu Q Z,Qian J,et al.Thermal effect analysis of 1560nm laser frequency doubling in a PPLN crystal[J].Chinese Journal of Lasers,2015,42(7):0708002.张远涛,屈求智,钱军,等.PPLN晶体1560nm激光倍频过程的热效应分析[J].中国激光,2015,42(7):0708002.
[6]Liu X,Shen X J,Yin J L,et al.Research on extending temperature acceptance bandwidth of second harmonic generation in cascaded crystals[J].Chinese Journal of Lasers,2018,45(1):0108001.刘恂,沈学举,殷建玲,等.级联晶体倍频器件温度适应性扩展研究[J].中国激光,2018,45(1):0108001.
[7]Cui Z J,Liu D A,Sun M Z,et al.Compensation method for temperature-induced phase mismatch during frequency conversion in high-power laser systems[J].Journal of the Optical Society of America B,2016,33(4):525-534.
[8]Cui Z J,Liu D A,Yang A H,et al.Temperatureinsensitive frequency conversion by electro-optic effect compensating for phase mismatch[J].IEEEPhotonics Journal,2016,8(5):1-8.
[9]Liu X,Shen X,Yin J,et al.Three-crystal method for thermally induced phase mismatch compensation in second-harmonic generation[J].Journal of the Optical Society of America B,2017,34(2):383-388.
[10]Zhang D X,Lu J,Feng B H,et al.Increased temperature bandwidth of second harmonic generator using two KTiOPO4crystals cut at different angles[J].Optics Communications,2008,281(10):2918-2922.
[11]Zhong H Z,Yuan P,Wen S C,et al.Temperatureinsensitive frequency tripling for generating highaverage power UV lasers[J].Optics Express,2014,22(4):4267-4276.
[12]Zhong H Z,Yuan P,Zhu H Y,et al.Versatile temperature-insensitive second-harmonic generation by compensating thermally induced phase-mismatch in a two-crystal design[J].Laser Physics Letters,2012,9(6):434-439.
[13]Brown M.Increased spectral bandwidths in nonlinear conversion processes by use of multicrystal designs[J].Optics Letters,1998,23(20):1591-1593.
[14]Hansen A K,Andersen P E,Jensen O B,et al.Highly efficient single-pass sum frequency generation by cascaded nonlinear crystals[J].Optics Letters,2015,40(23):5526-5529.
[15]Ji B,Zheng X S,Cai Z P,et al.Walk off compensation,multicrystal,cascaded,single pass,second harmonic generation in LBO[J].Laser Physics,2012,22(9):1401-1405.
[16]Smith A V,Armstrong D J,Alford W J.Increased acceptance bandwidths in optical frequency conversion by use of multiple walk-off-compensating nonlinear crystals[J].Journal of the Optical Society of America B,1998,15(1):122-141.
[17]Zondy J J,Kolker D,Bonnin C,et al.Secondharmonic generation with monolithic walk-offcompensating periodic structures II Experiments[J].Journal of the Optical Society of America B,2003,20(8):1695-1707.
[18]Smith A.Crystal nonlinear optics[M].New Mexico:AS-Photonic,2015:58-59.
[19]Hanson F,Dick D.Blue parametric generation from temperature-tuned LiB3O5[J].Optics Letters,1991,16(4):205-207.
[20]Yarborough J M,Falk J,Hitz C B.Enhancement of optical second harmonic generation by utilizing the dispersion of air[J].Applied Physics Letters,1971,18(3):70-73.