The dispersion of lines written in a turbulent jet flow

We write patterns, such as dots, lines and crosses, in a strongly turbulent air flow by fusing N2 and O2 molecules to NO, which is then used as a tracer. This photosynthesis is done in the focus of a strong UV laser (ArF excimer ¿ Physik, LPX 150). A while (tens of µs) later, the written patterns are made visible through inducing fluorescence with a second (UV) laser. The deformed and dispersed pattern of NO molecules is photographed in the UV using a fast intensified camera [1]. This technique allows us to create tracer patterns at will, and with sizes comparable to the smallest length scale in turbulence. This would have been very hard using seeded particles, such as in particle tracking velocimetry