Systems and methods for determining gas velocity based on phase differences of signals from two or more interaction paths in a gas analyzer system. A laser source, which can provide access to an absorption gas line, is expanded, or is split into two or more beams. These beams can be used to create two (or more) parallel sampling paths separated by a known distance. Gas travelling in the plane of the two beams of light will pass through the optical paths at two (or more) different times creating very similar signals that will be out of phase with each other. The amount of phase difference will be inversely proportional to the velocity of the gas.
