Two-dimensional imaging of OH in flames by use of polarization spectroscopy

Two-dimensional imaging of OH radicals in a premixed CH₄/O₂ flame by polarization spectroscopy is reported. Polarization spectroscopy was applied in a copropagating geometry with linearly polarized pump and probe beams. The images were measured with the laser frequency tuned to resonance with the Q₁(9) A²Σ−X²Π(0, 0) transition of OH. The signal dependence on the crossing angle between the pump and probe beams was also studied. The possibilities for two-dimensional temperature mapping were demonstrated by measuring images at two different rotational lines and by extracting the temperature map from these measurements.