  Segmented primary mirrors are indispensable to master the steady increase in
spatial resolution. Phasing optics systems must reduce segment misalignments to
guarantee the high optical quality required for astronomical science programs.
Modern telescopes routinely use adaptive optics systems to compensate for the
atmosphere and use laser-guide-stars to create artificial stars as bright
references in the field of observation. Because multiple laser-guide-star
adaptive optics are being implemented in all major observatories, we propose to
use man-made stars not only for adaptive optics, but for phasing optics. We
propose a method called the doublet-wavelength coherence technique (DWCT),
exploiting the D lines of sodium in the mesosphere using laser guide-stars. The
signal coherence properties are then used. The DWCT capture range exceeds
current abilities by a factor of 100. It represents a change in paradigm by
improving the phasing optics capture range from micrometric to millimetric. It
thereby potentially eliminates the need of a man-made mechanical pre-phasing
step. Extremely large telescopes require hundreds of segments, several of which
need to be substituted on a daily basis to be recoated. The DWCT relaxes
mechanical integration requirements and speeds up integration and
re-integration process.
