A new nonlinear Raman spectroscopy technique for trace-gas detection was proposed and demonstrated. The technique involved the use of a thermal-lens detection scheme to monitor thermal emission from the stimulated Raman process. We termed this technique thermal-lens Raman spectroscopy, and it was combined with a novel scheme involving a nonlinear Raman spectroscopy without a tunable laser. This technique was applied to detecting trace hydrogen molecules in the atmosphere by use of a pulsed Nd:YAG laser and a continuous-wave He–Ne probe laser. A detection limit of 9 parts in 10<sup>6</sup> was attained.
© 2000 Optical Society of America
(170.5660) Medical optics and biotechnology : Raman spectroscopy
(190.4180) Nonlinear optics : Multiphoton processes
(290.5910) Scattering : Scattering, stimulated Raman
(300.6390) Spectroscopy : Spectroscopy, molecular
(350.6830) Other areas of optics : Thermal lensing
Yuji Oki, Shinichiro Nakazono, Yuji Nonaka, and Mitsuo Maeda, "Sensitive H2 detection by use of thermal-lens Raman spectroscopy without a tunable laser," Opt. Lett. 25, 1040-1042 (2000)