稳定同位素比值的测量在地质学、气象学和地球科学的研究中具有重要的应用价值。水汽同位素丰度的测量对理解与干旱相关的同温层大气科学具有重要的意义。水汽分子在2.7μm 附近具有较强的吸收,适宜于高灵敏度光谱的测量。文章报道了利用差频技术(Difference frequency generation)和准相位匹配技术(Quasi-phasematching),将调谐范围在750～840nm 之间的连续可调谐钛宝石激光器和单频连续的Nd∶YAG激光器,耦合到周期性极化铌酸锂非线性光学晶体中,产生2.5～4μm 波段的中红外可调谐激光。选择周期为20μm 的PPLN晶体,产生2.7μm 附近的中红外差频激光,利用差频产生的中红外激光光源,具有窄线宽、宽调谐等优点。结合光程为100m 的Herriott型多通吸收池,采用直接吸收光谱方法测量了实验室大气中的水汽分子同位素,得到了同位素比值R及¹⁷O,¹⁸O,D的丰度值毮,实验所测R值与国际标准具有很好的一致性。

Stable-isotope ratio analysis of water is an important tool for geology, meteorology, and earth sciences. Measurements of water vapor isotopes are very helpful to explaining stratospheric aridity and related issues in atmospheric sciences. The absorption of water vapor near 2.7μm is very strong so it is suitable for measuring high sensitivity spectra. Based on difference frequency generation and quasiphase matching, by mixing an Nd∶YAG laser with Ti∶Sapphire tunable from 750 to 840 nm in a 50 mm long periodically poled lithium niobate(PPLN) crystal, a widely tunable CW laser source was generated for the midinfrared spectral range from 2.5 to 4μm. We chose A=20μm for PPLN crystal, the generated laser was around 2.7μm. This laser is widely tunable and of inherent narrow linewidth based on difference frequency generation. Using this idler laser and 100m multipasscell, and direct absorption the water vapor isotopes were measured in the laboratory air. The authors measured isotopes ratios and δ¹⁷O,δ¹⁸O and δ D. The values were found to be in excellent agreement with thestand ardvalue for three individual lines.