Flow velocity measurements using adaptive optics with a laser guide star

Laser optical techniques are widely used for flow velocity measurements, since they offer high temporal, spatial and velocity resolutions. However, optical wavefront distortions often deteriorate the measurement properties. Adaptive optics enables the correction of these disturbances. A Mach Zehnder interferometer is used to measure through a fluctuating liquid-gas phase boundary, which can lead to a misalignment of the interfering laser beams. In order to realize the adaptive interferometer the Fresnel reflex of the phase boundary is used as a Laser Guide Star (LGS) for the first time to the best of the authors’ knowledge. The LGS allows to measure the wavefront distortions induced by the fluctuating phase boundary. Two biaxial electromagnetically driven steering mirrors are employed to correct the wavefront distortions. This opens up the possibility for flow measurements through a dynamic phase boundary in order to investigate turbulence phenomena.