High-power continuous-wave mid-infrared radiation generated by difference frequency mixing of diode-laser-seeded fiber amplifiers and its applicationto dual-beam spectroscopy

We report the generation of up to 0.7 mW of narrow-linewidth (<60-MHz) radi ation at 3.3 mu m by difference frequency mixing of a Nd:YAG-seeded 1.6-W Y b fiber amplifier and a 1.5-mu m diode-laser-seeded 0.6-W Er/Yb fiber ampli fier in periodically poled LiNbO3. A conversion efficiency of 0.09%/W (0.47 mW W-2 cm(-1)) was achieved. A room-air CH4 spectrum acquired with a compa ct 80-m multipass cell and a dual-beam spectroscopic configuration indicate s an absorption sensitivity of +/-2.8 x 10(-6) (+/-1 sigma), corresponding to a subparts-in-10(9) (ppb) CH4 sensitivity (0.8 ppb). (C) 1999 Optical So ciety of America.