A new optical approach for entrainment detection is presented using a measurement probe, which is applicable at different axial and radial positions within the column in an industrial environment. The new developed probe enables in-line detection and on-line analysis of entrained droplets between separation stages respectively at the column head. Different test rigs (up to DN 450) are used for data sampling. The new construction of the probe uses a purge gas stream to protect the front window of the probe from wetting, providing a non-wetted and clear view, leading to better image qualities and low purge medium consumption. A comparison of the measurement results with the Phase-Doppler-Anemometry shows a good agreement. As expected, entrainment depends on liquid and gaseous flow rates. Capability of models from literature to cope with the available data are discussed.