We report the generation of up to 0.7 mW of narrow-linewidth (<60-MHz) radiation at 3.3μm by difference frequency mixing of a Nd:YAG-seeded 1.6-W Yb fiber amplifier and a 1.5-μm diode-laser-seeded 0.6-W Er/Yb fiber amplifier in periodically poled LiNbO<sub>3</sub> . A conversion efficiency of 0.09%/W (0.47 mWW<sup>-2</sup> cm<sup>-1</sup>) was achieved. A room-air CH<sub>4</sub> spectrum acquired with a compact 80-m multipass cell and a dual-beam spectroscopic configuration indicates an absorption sensitivity of ±2.8 × 10<sup>-5</sup> (±1σ), corresponding to a sub-parts-in- 10<sup>9</sup>(ppb) CH<sub>4</sub> sensitivity (0.8 ppb).
© 1999 Optical Society of America
(060.2320) Fiber optics and optical communications : Fiber optics amplifiers and oscillators
(190.2620) Nonlinear optics : Harmonic generation and mixing
(280.3420) Remote sensing and sensors : Laser sensors
(300.6340) Spectroscopy : Spectroscopy, infrared
D. G. Lancaster, D. Richter, R. F. Curl, F. K. Tittel, L. Goldberg, and J. Koplow, "High-power continuous-wave mid-infrared radiation generated by difference frequency mixing of diode-laser-seeded fiber amplifiers and its application to dual-beam spectroscopy," Opt. Lett. 24, 1744-1746 (1999)