Simulation of closed tip tilt loop observations on a 5 meter telescope

Here is a movie showing simulations of the point spread function resulting from the propagation of electromagnetic radiation through a 6 layer Cerro Pachon model and compensation by a tip tilt mirror. This simulation used electromagnetic radiation of .5 microns to sense wavefront tip tilt errors using a Shack Hartmann wavefront sensor. The wavefront sensor had 16 subapertures across the telescope pupil, each of size 31.25 cm. This simulation performed a diffractive propagation of the wavefront through a lenslet array to form the Shack Hartmann spots. The average x and y centroids were then used to drive a tip tilt mirror. This tip tilt mirror was used to correct both the .5 micron radiation used for sensing and 2 micron radiation, which was then used to form a detected image. Wavefronts were propagated every 10 milliseconds, and this was also the update interval for the tip tilt mirror. The wavefronts were propagated through the atmosphere using geometric propagation.

Closed tip tilt loop simulation

On the left is shown the open loop electromagnetic field amplitude. On the right is shown the closed loop electromagnetic field amplitude. The cross-hairs indicate the center of the image. The simulation time is printed in the upper left corner of the movie.

The parameters for this simulation were:
Aperture diameter 5 meters
Sensing wavelength .5 microns
Detection wavelength 2 microns
r0 of .16 meters at .5 microns
2 cm pixel scale in the wavefront
2 cm pixel scale in the turbulence layer
10 millisecond timesteps for the tip tilt mirror control and wavefront propagation
10 second duration for the simulation (total of 1000 10 millisecond timesteps)

This simulation required about 30 minutes to form the 6 layers used to model the turbulent atmosphere. Each timestep required about 5.5 seconds to perform all propagations and control. Thus the entire simulation required about 2 hours. The peak RAM usage for this simulation was about 1 Gigabyte.

This simulation was generated using the program palao_simulation, which is provided as part of the Arroyo distribution.