Laser guide stars created in the earth's sodium layer are the choice for all ELTs as adaptive optics reference. With the
thickness of the sodium layer spanning up to 10km, the apparent image of the guide stars on the adaptive optics
wavefront sensors is elongated. The further away sub-apertures of the WFS are from the guide star launch location, the
more elongated the guide star appears on the sensor. To counteract the decreased signal from the elongation, usually an
increased laser power is demanded or special format radial CCDs are proposed. Another known possibility is to utilize
pulsed lasers and follow dynamically the propagating pulse on its way through the sodium layer, creating a sharp spot at
the wavefront sensor location. Similar processes have been used for laser guide stars created with Rayleigh scattering in
the lower atmosphere, increasing greatly the number of photons that can be received from the guide star.
We present here the design and first laboratory tests of such a dynamically refocus device, based on membrane mirrors.
Driven acoustically at high frequencies the stroke and phase of the mirror can be controlled. With a compact appearance
the system seems to be easy to use and could enable precise wavefront control with lower power pulsed lasers at ELTs
and other telescopes.
© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
S. Rabien and J. Ziegleder
Dynamical refocusing laser guide stars with membrane mirrors
", Proc. SPIE 8447, Adaptive Optics Systems III, 84474P (September 13, 2012); doi:10.1117/12.926537; http://dx.doi.org/10.1117/12.926537