Tunable continuous wave DFG-based gas sensor using fibre amplified 1.5 mu m external cavity diode laser and high power 1 mu m diode laser

A novel compact, room-temperature mid-infrared difference frequency generat ion (DFG)-based trace gas sensor based on direct absorption spectroscopy is reported. Tunable, narrow linewidth difference frequency radiation from 3. 3 to 3.5 mu m is generated in periodically pored lithium niobate at power l evels of > 4 mu W. The output from an external cavity diode laser, amplifie d up to 20dBm by an erbium-doped fibre amplifier is used as the signal sour ce. A 500 mW alpha-DFB diode laser at 1066nm serves as the DFG pump source. This sensor has been applied to real time trace gas detection of CH4 and H 2CO.