Spectroscopic detection of methane by use of guided-wave diode-pumped difference-frequency generation.

We report spectroscopic gas detection by the use of mid-infrared difference-frequency mixing of two diode lasers in a channel waveguide. The waveguide was fabricated by annealed proton exchange in periodically poled lithium niobate. We generated 3.43-3.73-microm tunable radiation in a single waveguide at room temperature by mixing diode lasers near 780 and 1010 nm. High-resolution spectra of methane were obtained in 2 s with electronically controlled frequency scans of 45 GHz. The use of highly efficient waveguide frequency converters pumped by fiber-coupled diode lasers will permit construction of compact, solid-state, room-temperature mid-infrared sources for use in trace-gas detection.