7 July 2000 Tracking the global tilt using tails of radio guide stars
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Abstract
The problem of global tilt arises when the downgoing light from an artificial guide star traces in reverse the upgoing laser beam. The problem also exists if the upgoing beam is in the radio, since we still cannot determine its absolute position to the required accuracy. We propose a way to solve this problem by tracing the tails of the artificial guide star. Radio pulses breaking down the air into visible plasma create the beacon, and each pulse uses the residue plasma of its predecessor to restart the break down. As the radio beams wander on their way up, the new spot will not overlap perfectly with the previous one. Thus, the spot will have a small trail, which can help trace the history of the tilt. Comparison of the measurement of the previous pulse to the tail of the new one will provide the differential movement of the downgoing beam. Integrating this movement will yield the absolute pulse location. Cumulative errors are reduced by comparison to weak nearby natural guide stars. We ran simulations of the process, where we include random atmospheric tilts for the radio beam. We also checked the effect of intentional nutations of the upgoing beam and the effects of atmospheric winds on the plasma spot, as well as detection noise. We fitted the measured signal to the head and tail of each spot, and found their difference, which amounts to the change in tilts since the last pulse. We integrated this difference to find the absolute tilt. We show that indeed the tail trail can be traced to yield information about the tilt.
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Erez N. Ribak, Roberto Ragazzoni, Vadim A. Parfenov, "Tracking the global tilt using tails of radio guide stars", Proc. SPIE 4007, Adaptive Optical Systems Technology, (7 July 2000); doi: 10.1117/12.390319; https://doi.org/10.1117/12.390319
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KEYWORDS
Stars

Plasma

Atmospheric plasma

Telescopes

Light scattering

Interferometers

Laser guide stars

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