The practicality of a compact solid-state laser-based difference frequency generation system is demonstrated as a tool for probing hydrocarbon-based plasmas. The laser light of a cw Nd : YAG operating at 1064 nm and one of two distributed feedback diode lasers operating at 1560 and 1620 nm were mixed in a periodically poled lithium niobate crystal producing mid-infrared radiation at 3.35 and 3.1 µm for the detection of CH4 and C2H6 at the first wavelength and C2H2 and C2H4 at the latter. The radiation was used to probe a rf capacitively coupled CH4 plasma for a matrix of conditions, varying power (<180 W) and pressure (<1 Torr) in both direct absorption spectroscopy and wavelength modulation spectroscopy (WMS) experiments to achieve relatively high sensitivities while retaining accurate spectral information in the form of linewidths. A minimum detectable absorption coefficient αmin of 2 × 10−5 cm−1 was achieved for direct absorption spectroscopy which corresponds to a minimum detectable density for CH4 of 1.7 × 1012 cm−3 and an αmin value of 2 × 10−6 cm−1 was achieved for WMS measurements on C2H2. The depletion of CH4 was measured to increase from 23% at 40 W to 40% at 180 W at a pressure of 0.84 Torr, and the depletion increased to 56% as the pressure decreased to 0.45 Torr.