Raman mixture composition and flow velocity imaging with high repetition rates

A novel and completely tracer free strategy to image composition and velocity fields during the mixing process of two liquids is introduced. The achieved temporal resolution, spatial resolution and sampling rate of 30 ns, 54 x 54 mu m(2) and 10 kHz, respectively, are sufficient to resolve Kolmogorov time and length scales as well as transient mixing phenomena of many technical mixing processes. During the injection of liquid water into liquid ethanol, mixing was quantitatively observed by means of high repetition rate Raman imaging using a laser cluster for the excitation of the Raman process with 8 successive light sheet pulses. One high speed camera was used to detect the CH-vibration Raman band signal of ethanol, while a second one was used to detect the OH-vibration Raman band signal of water and ethanol. From the ratio of both, the mixture composition field was computed. The dense flow field was determined by processing the mixture composition images with a variational optical flow method. (C) 2010 Optical Society of America