The set-up of the MM-LDA used in this work is depicted schematically in Fig. 2. It consists of a 635 nm broad-area laser diode coupled to a multi-mode fiber. The resulting multi-mode light is focused onto a beam splitting grating via a Keplerian telescope. A second Keplerian telescope focuses the first diffraction orders to form the measurement volume inside the intersection. The sensor was examined by calibration measurements. The length of the intersection amounted to 2∙lz = 2.1 mm, whereas the axial spatial resolution, given by the length of interference volume 2∙az, is 65 μm. The system was designed for the detection of back-scattered light of fluorescent seeding particles to allow for near-wall flow measurements by suppressing wall reflexes using an optical filter, at the expense of a moderate loss of signal-to-noise ratio due to lower scattered light intensity. In this work, polystyrene particles (dpar = 2.07 mm, Microparticles GmbH) doped with a fluorescent dye (Nile Blue A, ex/em 635/685 nm) were used to investigate water flows in the respective experiments.