Dual wavelength digital holography for 3D particle image velocimetry S. Grare, S. Coëtmellec, D. Allano, G. Grehan, M. Brunel and D. Lebrun J. Eur. Opt. Soc.-Rapid Publ., 10 (2015) 15009 Published online: 21 February 2015 DOI: 10.2971/jeos.2015.15009