The OLEX system on board of the research aircraft Falcon is a vertically upward pointing 4-wave-length lidar. It consists of two lidar transmitters. One is a Nd:YAG laser with second and third harmonic generation (i.e. 1064nm, 532nm, and 355nm). The other one is a Xe:Cl excimer laser emitting at 308nm. The two UV wavelengths (308nm and 355nm) are used to retrieve stratospheric ozone profiles from about 2 km above the flight level to 26 km altitude by means of the differential absorption lidar (DIAL) technique. From the ratio of the backscatter signals at these two wavelengths - one of them is being absorbed by ozone while the second is not - profiles of ozone number density can be calculated. Furthermore, the returns at the three Nd:YAG wavelengths contain information about the size distribution of the scattering particles. The capability to measure the cross polarised return at 532 nm allows for phase discrimination, i.e. ice/water discrimination and PSC classification.