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tokens: a small fraction of the light to the photon counter of the profiling subsystem. In an AO system, typically about 97 per cent of the light of the LGS is directed towards the WFS by a beam splitter. The remaining 3 per cent of the light from the LGS follows the path to the science camera. This fraction could be notch-filtered and redirected to a high-speed photon counting detector, used to measure sodium density profiles. While the retrieved profiles taken at the LZT demonstrate that the CW lidar profiles are consistent with the ‘standard’ lidar profiles, our results obtained with a large area APD sensor used in linear mode were affected by a robust radio-frequency interference. In a photon-noise limited case the CW lidar method should have provided profiles with an accuracy of 20–40 m RMS centroid offset. Instead, the spread found in our experimental data is of the order of 150–200 m. We believe that this discrepancy is due to electromagnetic interference in the linear APD signal detected. Our theoretical analysis and the numerical simulations show the potential of the method. The method could yield sodium centroid profiles with high accuracy. Different scenarios could be realized, either one LGS modulated with a higher modulation strength (>60 per cent) or multiple LGS modulated with low modulation strength (≈30–40 per cent) could be used. We note that laser amplitude modulation strengths of 30–40 per cent result in 15–20 per cent decrease in the LGS return flux, which can be acceptable already with current 22W CW sodium lasers. Recent experiments done at the ESO WLGSU in La Palma (Haguenauer, Boanccini Calia Pfrommer 2019 ) have demonstrated the feasibility of splitting the uplink laser beam in two, to create two LGS angularly separated. The subsequent reduction of 50 per cent of the LGS flux corresponds to the loss of power due to a modulation of 100 per cent (ε = 1), in our CW lidar. The multiconjugate AO system at Gemini South (GeMS) splits one 20W CW laser into five LGS which reduces the return flux from one LGS to 20 per cent. For the new AO system under development for Gemini North, it is planned to split one 20W CW laser into two LGS. Calculations in the frame of the ESO Mavis project Phase A study indicate that using the 20W CW lasers in the VLT Galacsi LGS-AO system, with 20 × 20 cm sub-apertures Shack-Hartmann wavefront sensor, will still be able to support MCAO systems at visible wavelengths. Considering also that RD work is in place at ESO to both, enhance the LGS return flux by frequency chirping, and by increasing the laser power beyond 50 W at 589 nm, there is a good outlook for the CW lidar method to be used in operations, turned on when necessary. As this is the time of designing the extremely large telescope AO systems, we solicit the system experts to take provisions for the CW lidar implementation into account. Besides providing sodium laser profiles and abundances on time-scales of several seconds, of general use