Laser-based volumetric colour-coded three-dimensional particle velocimetry

We present a method of three-dimensional particle velocimetry with a single digital colour camera using multiple colour illumination to encode image depth over a large volume. A copper vapour laser operating at 511 nm is used to pump an optical fibre producing a multiple-wavelength beam via multiple order stimulated Raman scattering. The beam is dispersed and formed into a stack of thin sheets to illuminate a volume of space. The spatial co-ordinates of particles imaged within the illuminated volume are obtained from their imaged x, y positions with depth discerned from particle hue (set by the wavelength of illumination). The method exhibits an RMS depth error of 3% in relation to the thickness of the illuminated region. This paper reports a proof-of-principle of three-dimensional particle imaging using a multi-wavelength laser source with a view to 3D-3C particle velocimetry.