A target gas sensing system includes a single source at a first location for generating two light beams having first and second frequencies wherein the difference between the first and second frequencies is the Raman frequency of the target gas. A difference frequency generator outputs the two light beams having the first frequency, the second frequency, and a third light beam having a third frequency that is the difference between the first and second frequencies. The first, second, and third light beams are directed toward the target gas. An input optic directs light from the third light beam, after interacting with the target gas, to a receiver for absorption spectroscopy processing, directs a fourth light beam from the target gas to a receiver for coherent anti-Stokes Raman processing, wherein the fourth light beam has a frequency of twice the first frequency minus the second frequency.