Method and device for laser doppler measurement of a velocity field of a fluid flow

A laser Doppler method for measuring a velocity field of a fluid flow comprises the steps of: illuminating a light-section (4) extending through the fluid flow with laser light; converting spatial distributions of Doppler frequency shifts of scattered light, which is scattered by particles carried by the fluid flow out of the light-section (4) in different scattering directions, into a spatial light intensity distribution for each scattering direction; normalizing the spatial light intensity distributions in respect of a light intensity distribution of the scattered light; subtracting the normalized spatial light intensity distributions obtained for the different scattering directions in pairs to obtain a spatial light intensity difference distribution for each pair of the different scattering directions; defining coordinate axes by the directions of difference vectors of pairs of wave vectors (k) of the scattered light pointing in the different scattering directions; and quantitatively determining a projection of the velocity field of the fluid flow in the light-section on each coordinate axis (x, y, z) from the corresponding spatial light intensity difference distribution divided by the modulus of the corresponding difference vector.