Abstract
We have developed an efficient and compact 3.4 μm difference-frequency-generation spectrometer using a 1.55 μm distributed feedback (DFB) laser diode, a 1.06 μm DFB laser diode, and a ridge-waveguide periodically poled lithium niobate. It is continuously tunable in the 30 cm(-1) span and is applied to (12)CH(3)D/(12)CH(4) isotope ratio measurements. The suitable pair of (12)CH(3)D ν(4) (p)P(7,6) and (12)CH(4) ν(2)+ν(4) R(6) F(1)((1)) lines enabled us to determine their isotope ratio with a precision repeatability of 0.8‰ using a sample and a working standard of pure methane with an effective signal averaging time of 100 ms.