%0 Journal Article %T An Efficient and Compact Difference-Frequency-Generation Spectrometer and Its Application to 12CH3D/12CH4 Isotope Ratio Measurements %A Kiyoshi Tsuji %A Hiroaki Teshima %A Hiroyuki Sasada %A Naohiro Yoshida %J Sensors %D 2010 %I MDPI AG %R 10.3390/s100706612 %X We have developed an efficient and compact 3.4 ¦Ìm difference-frequency-generation spectrometer using a 1.55 ¦Ìm distributed feedback (DFB) laser diode, a 1.06 ¦Ìm DFB laser diode, and a ridge-waveguide periodically poled lithium niobate. It is continuously tunable in the 30 cm¨C1 span and is applied to 12CH3D/12CH4 isotope ratio measurements. The suitable pair of 12CH3D n4 pP(7,6) and 12CH4 ¦Í2+¦Í4 R(6) F1(1) lines enabled us to determine their isotope ratio with a precision repeatability of 0.8¡ë using a sample and a working standard of pure methane with an effective signal averaging time of 100 ms. %K isotope ratio %K methane %K laser spectroscopy %K difference frequency generation %K waveguide PPLN %U http://www.mdpi.com/1424-8220/10/7/6612