摘要
为了提升532 nm激光的产生效率和功率稳定性,以基于倒格矢实现准相位匹配的手段为基础,设计了合适的啁啾周期极化铌酸锂(CPPLN)晶体的结构并进行仿真,采用自制的1064 nm激光器对该结构的晶体进行腔外倍频实验。在输入的1064 nm连续光功率为22.53 W的条件下可以获得功率为148 mW、波长为532 nm的光,光光转换效率约为0.66%,是三硼酸锂(LBO)的15.58倍。进一步验证了CPPLN晶体的温度鲁棒性,532 nm倍频光的功率关于温度的半峰全宽为8.40℃,且在该范围内功率呈现振荡的趋势,其原因是加工精度的限制导致倒格矢分布不连续。所得到的输出倍频光的光斑为标准的高斯光斑,其并不受温度的影响。结果表明,该设计结构的CPPLN晶体相对于传统LBO晶体具有更高的倍频效率与温度鲁棒性。
Objective The 532 nm solid-state laser is one of the most widely used lasers in current industry and scientific research.The most common route to build a 532 nm solid-state laser system is to generate a 1064 nm laser by pumping Nd∶YVO4 or Nd∶YAG crystal with 808 nm/880 nm laser diode,and then generating continuous or pulsed 532 nm lasers by secondharmonic generation(SHG)through frequency doubling crystal.At present,the most common frequency doubling crystal is lithium borate(LBO),which is superior in low cost,high damage threshold,and wide transmittance bands.However,due to the low nonlinear coefficient of LBO and the temperature phase matching scheme,the SHG efficiency is low and highly sensitive to temperature.In this study,we design and simulate a suitable structure of chirped periodically poled lithium niobate(CPPLN)that exhibits certain quasi-phase matching bandwidth and large effective nonlinear coefficient,and a CPPLN crystal with designed structures is applied for extra-cavity SHG experiment with a home-made 1064 nm laser.The result shows that the CPPLN with a designed structure has better SHG efficiency and temperature robustness compared with the traditional LBO crystal.The findings are expected to be helpful to the design of the 532 nm laser as well as to the power and temperature robustness improvement at other wavelengths.Methods We first analyze the coupling equation of the SHG,which shows that a larger gain bandwidth of the CPPLN crystal leads to better temperature robustness but lower SHG efficiency.According to the analysis,we design the structure of the CPPLN crystal after measuring the bandwidth of the input light.To visualize the effect of the designed CPPLN crystal,the Fourier transform of the effective Fourier coefficients of the crystal is taken to get their distribution in the reciprocal lattice vector domain.The above measures have led to the design of a CPPLN crystal structure that combines good temperature robustness with a high frequency doubling efficiency.To verify the actual result of this crystal,we build a frequency doubling experimental device based on a homemade 1064 nm laser with precise temperature control.To this end,an experiment is conducted under different temperatures by analyzing the variations of the output power and the spot shape of the 532 nm laser.The results demonstrate the practicality of the designed CPPLN crystal.Results and Discussions In the simulation,the reciprocal lattice vectors provided by the designed CPPLN crystals compensate for the phase mismatch under temperature conditions from 13.84 to 27.24℃(Fig.2).In other words,the SHG efficiency will be maintained all the time at a high level with the designed CPPLN.In the SHG experiment,the data of the SHG power of the CPPLN under different temperature conditions are consistent with the fitted curves[Fig.4(a)].Under the condition of 22.53 W input power of 1064 nm continuous wave,the power of 148 mW of 532 nm light is obtained,which corresponds to the optical-optical conversion efficiency of about 0.66%,15.58 times that of LBO[Fig.4(b)].Moreover,the temperature gap in which the power of the 532 nm decreases to half is 8.40℃,ranging from 24.19 to 32.59℃,fairly larger than the LBO scheme(Fig.5).The difference between this temperature range and the simulated result is caused by the error in crystal processing,and so is the curve oscillation in this temperature range.Besides,as a standard Gaussian spot,the output spot is unaffected by temperature(Fig.8).Conclusions In this study,we design and fabricate the CPPLN of a novel structure to improve the 532 nm generation efficiency as well as temperature robustness.The SHG performance of the designed CPPLN is analyzed both theoretically and experimentally,compared with LBO.In the simulation,the SHG efficiency of the CPPLN with designed structure is over 20 times higher than that of LBO and is stable within a temperature gap of more than 10℃.In the experiment,with the CPPLN fabricated in the designed structure,the power of 148 mW of 532 nm light is obtained under the condition of 22.53 W 1064 nm continuous wave,with an optical-optical conversion efficiency of about 0.66%,15.58 times higher than that of LBO.In addition,the full width at half-maximum of the SHG power of the designed CPPLN about temperature is 8.4℃,quite larger than that of LBO.Since the error of crystal processing can only reach 10 nm at the minimum,the crystal structure of the fabricated CPPLN remains slightly different from the designed one,causing the difference between the actual temperature stabilization range and the designed range,and the oscillation of SHG power curve about temperature.It is believed that with the optimization of the polarized crystal process,the error will be reduced and the CPPLN performance will be further improved.The CPPLN with the designed structure is promising in the field of Ti∶Sapphire femtosecond laser,narrow linewidth laser,and low noise laser.
作者
苏伟伦
刘峻铭
邹娱
刘励强
洪丽红
李志远
Su Weilun;Liu Junming;Zou Yu;Liu Liqiang;Hong Lihong;Li Zhiyuan(School of Physics and Optoelectronics,South China University of Technology,Guangzhou 510641,Guangdong,China;Guangdong Jingchuang Optical Machinery Co.,Ltd.,Guangzhou 510510,Guangdong,China;State Key Laboratory of High Field Laser Physics,Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences,Shanghai 201800,China)
出处
《光学学报》
EI
CAS
CSCD
北大核心
2024年第11期187-195,共9页
Acta Optica Sinica
关键词
非线性光学
啁啾周期极化铌酸锂晶体
温度鲁棒性
腔外倍频
nonlinear optics
chirped periodically polarized lithium niobate crystal
temperature robustness
extracavity frequency doubling
