Large Dynamic Range Co-Phasing System Development for Segmented Telescope Mirrors Piston and Tip/Tilt expected errors The initial error after deployment is considered to be +/- 100µm PSF Entrance pupil MTF PTF (Piston) PTF (Tip/Tilt) OTF (3 sub pupils) 2π Ambiguity (Range –λ/2,+λ/2) III. Multi-Wavelength measure By taking 3 different PSF at 3 different λ and processing it into 3 different PTF, it is possible to increase the measurement dynamic range. Once the 3 measures have been performed, 3 different piston errors can be processed into an unwrapping procedure algorithm. With this treatment, it is possible to measure piston errors two or three orders of magnitude bigger than the single λ measure. The total range of 3 λ measure is called synthetic lambda (λs) and the final range is within –λs/2,+λs/2 limits. λs is calculated with the next equation: (1/λ1-2/λ2+1/λ3)^(-1) Taking λ = 630,650 and 670nm, λs = 342 µm Simulation shows that for an initial piston of 140 µm and 10 µm and initial tilt of X and Y of 10 µrad, the algorithm recovers the values within a 1 nm. The algorithm demonstrates the feasibility of such a technique. I. Introduction Space segmented telescopes are placed in orbit with phase errors between each segment inherent to the segmentation. This errors must be corrected in order to obtain the maximum resolution of the instrument (diffraction limited). The maximum tolerated errors must be less than λ/40, that is to say, around 10nm in the visible spectrum. After the deployment of the telescope into orbit, there is an initial error of +/- 100µm. This error is times larger than the expected error (10nm). To co-align the segments, it is necessary to implement a sensor sensitive to 10nm but with a range of 100µm. This sensor must be sufficiently light and robust to be placed in a Space instrument. Next, it is explained the sensor algorithm that will allow to implement a complete sensor system. II. Phase retrieval This method is used in several applications. It consists in taking one photo of the entrance pupil Point Spread Function (PSF), and analyzing this to retrieve the phase in all different sub pupils, all of them referenced to one of them. When PSF is taken with a CCD device, it is transformed into its OTF via a FFT (Fast Fourier Transform) algorithm. OTF provides two different information, first one is the MTF (Modulation Transfer Function) and second one is the PTF (Phase transfer function) All phase information is encoded into the PTF, and it can be decoded by taking peak values and linearly combining them. This procedure can be performed within several sub pupils configuration. This project is aimed to be used in a 7 sub pupil configuration, but for the sake of clarity, only 3 sub pupil configuration is showed here. A major problem encountered with this method, is that it is only possible to measure distances within a range of -λ/2,+λ/2 of the incoming electromagnetic field. Juan F Simar – ARC Phd Student, Yvan Stockman – Project Manager Centre Spatial de Liège Université de Liège