利用宽带倍频特性精确测量准相位匹配晶体的极化周期
Accurate measurement of grating period of periodically poled crystal by using broad band chirp pulse second harmonic generation
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摘要: 提出了利用准相位匹配晶体进行宽带脉冲倍频，再根据准相位匹配晶体的极化周期与倍频脉冲输出中心波长的相位匹配关系来精确测量准相位匹配晶体极化周期的新方法。理论分析了准相位匹配晶体的极化周期与倍频脉冲的光谱关系、倍频容许带宽与晶体长度的关系。研究表明：宽带脉冲倍频后输出的脉冲峰值波长对应于角度的调谐曲线具有对称性；对于长度为10 mm的极化晶体，其倍频容许带宽不到0.2 nm。实验中，采用了国产PPKTP晶体试验片，晶体尺寸为10 mm×7 mm×1 mm，理想极化周期9 300 nm。结果表明：对于中心波长为537.25 nm的倍频光，其对应的实际晶体极化周期为9 303.9 nm，大于晶体加工时的理想值；当倍频脉冲光谱测量精度为0.01 nm时，准相位匹配晶体的极化周期测量精度达到0.1 nm，远高于一般光学显微镜的观测精度。Abstract: According to quasi-phase matching relationship between the second harmonic center wavelength and the grating period length of periodically poled crystal, a new experimental method to measure the grating period of periodically poled crystal accurately was presented by using broad band chirp pulse second harmonic generation technique. The relationships between the second harmonic center wavelength and the grating period, the spectra bandwidth and the crystal length were analyzed theoretically. The grating period of PPKTP crystal with the size of 10 mm×7 mm×1 mm was measured experimentally. The results show that the real grating period is 9 303.9 nm depending on the second harmonic central wavelength of 537.25 nm, while the theoretical one is 9 300 nm. The method advances the measurement p
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