The image shows a two-dimensional Bunsen flame using methane at equivalence ratio of phi = 1.2. Blue flame luminosity due to emission from CH and C2 radicals, green particle tracks due to scattering from MgO particles under 6kHz excitation of a Cu-Vapor laser. FUJI 1600 ASA film.

Reference:

Tarek Echekki & M. G. Mungal (1990), "Flame Speed Measurements at the Tip of a Slot Burner: Effects of Flame Curvature and Hydrodynamic Stretch," Twenty-Third Symposium (Int.) on Combustion, The Combustion Institute, 455-461.