Difference frequency generation using one 1.58-μm and two 1.06-μm distributed feedback Bragg-grating laser diodes and a ridgetype PPLN alternately provide two 3.2-μm coaxial waves resonant with individual isotopic transitions separated by 13 cm-1. The ν3 band R(6) A2 allowed transition of 13CH4 and the ν3 band R(6) A2 weakly allowed transition of 12CH4 are an ideal pair for isotope ratio measurements. The 13CH4/12CH4 isotope ratio is determined for three sample gases with a relative uncertainty of 0.7 ‰, and it is confirmed that the temperature dependence is smaller than the uncertainty.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics