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A simple, compact sensor involving a continuous-wave 3.38 μm distributed feedback laser in combination with a novel compact dense-pattern multipass cell was demonstrated for simultaneous measurement of atmospheric methane and water vapor. The calibration-free direct absorption spectroscopy approach was adopted for data generation and processing. Allan deviation analysis indicates that minimum detection limits (1σ) of 11.0 ppb for CH4 and 100 ppm for H2O were achieved with a 1-s integration time at an optimum pressure of 50 Torr. Atmospheric environmental mixing ratios of these two gases were recorded and analyzed. This newly developed mid-infrared dual-gas sensor is very suitable for trace gas sensing in weight-limited unmanned aerial vehicle- or balloon-embedded field observations.

A continuous-wave mid-infrared radiation from difference frequency generation by mixing a continuous-wave Ti: sapphire laser and a continuous-wave YAG laser in a 15 mm long BaGa4Se7 crystal is demonstrated for the first time. The tunable range from 3.15 to 7.92 μm was achieved by rotating the crystal to fulfill the type I phase-matching condition. A maximum DFG power of 1.41 μW was obtained at 5 μm. Meanwhile the experimental DFG power conversion efficiency was 20.2 μW/W2, with a length-normalized slope efficiency of 15.5 μW/cmW2. The conversion efficiency decreases rapidly from 50 μW/cmW2 at 3.15 μm to 1 μW/cmW2 at 7.92 μm. The wavelength acceptance bandwidth and the angular acceptance bandwidth were measured to be 16.4 cm−1 and 44′ for DFG at 5.1 μm, respectively.