Objective: The objective of the activity is to develop a Polychromatic Laser Guide Star (PLGS) system to measure and compensate allwave-front distortions in an optical feeder links to terabit telecommunication satellites. This includes tip/tilt, or uplink beam wander, that is not directly measurable otherwise. Targeted Improvements: Being able to measure Tip/Tilt, in addition to higher orderwave-front aberrations, has a 75% improvement on the quality of service of an optical feeder link system. Description: Monochromatic Laser Guide Star (MLGS) Concept is a key enabling technology of Adaptive Optics (AO), making it possible to estimate the atmospheric distortion, in any direction. It consists in propagating a powerful laser from ground to the mesosphere (90km altitude) to excitea specific transition of Sodium atoms and create a shining spot in the sky at this specific wavelength. This artificial star can beused as a reference beacon to estimate and compensate the atmospheric turbulence. Unfortunately, even though the MLGS is promising approach and already used in most of the state-of-the-art astronomical telescopes, one major drawback lies in the fact that the low wavefront error modes (Tip/Tilt), accounting for >85% of the total distortion, cannot be estimated by this technique. This is due tothe fact that the wavelength of the outgoing beam (i.e. that of the MLGS) is the same as that of the incoming beam (i.e. the photons emitted by the artificial star), hence the Tip/Tilt of both beams is cancelled out and cannot be inferred.To cope with this critical limitation, the present activity aims at exploring the Polychromatic Laser Guide Star (PLGS) approach. As opposed to a Monochromatic Laser Guide Star(MLGS), the main idea of the PLGS consists in producing an artificial star shining at several distinct wavelengths (ranging from UV to IR) by exciting various transitions of the mesosphere Sodium atoms. In this case, each wavelength emanating from the artificial star is deviated in a different way due to the slight chromaticity of the atmosphere. A receiver is used on ground to detect one spot per wavelength. The true Tip/Tilt can then be deduced from the differential Tip/Tilt between two distinct wavelengths. This activity will address the main challenges, namely, the return flux needs to be high enough to achieve a good Signal toNosie Ratio (SNR) at several distinct wavelength, the differential Tip/Tilt needs to be measured accurately to infer the true Tip/Tilt, the best laser format is not yet optimized, high power laser(s) might be necessary.Procurement Policy: C(2) = A relevant participation (in terms of quality and quantity) of non-primes (incl. SMEs) is required. For additional information please go to: http://www.esa.int/About_Us/Business_with_ESA/Small_and_Medium_Sized_En…

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