In a collaboration with Cranfield University we have used two-photon fluorescence microscopy to image the mixing of two flows - one of pure water and the other containing dye in solution.

The technique allowed us to obtain a PLIF-like image using only one access window, unlike conventional PLIF which normally requires as many as 3 windows because the light-sheet must be coupled into the flow at 90 degrees to the observation direction.

The figure opposite shows a conventional PLIF image with two-photon images shown as insets.  Concentration is shown below but mixing efficiency is also revealed using a RMS image (not shown).

Two-photon fluorescence has also been demonstrated in acetone vapour (see opposite), suggesting that two-photon flow imaging could be extended to the gas phase.