A widely tunable (5–12.5 μm) continuous-wave mid-infrared laser spectrometer based on difference frequency generation in AgGaS2

A widely tunable (5–12.5 μm) continuous-wave (cw) mid-infrared (mid-IR) laser spectrometer based on difference frequency generation (DFG) by mixing an external-cavity diode laser (ECDL) with a Ti:Sapphire laser in an AgGaS2 crystal is described. The wide tunability was achieved by tuning laser wavelength associated with crystal angle tuning under type II phase matching condition. A maximum output power of about 66 nW was obtained at 8.06 μm. High resolution spectrum of methane (CH4) over more than 10 cm−1 near 7.7 μm has been recorded to evaluate the performance of the developed DFG-based mid-IR laser spectrometer.