8.2 Kiepenheuer Institute Adaptive Optics System (KAOS)
The Kiepenheuer Institute Adaptive Optics System has been operating at the 70 cm Vacuum
Tower Telescope (VTT) on Tenerife, Spain, since 2002 (von der Lühe et al., 2003). The system
is very similar in design and implementation to the SST system in that it uses a correlating
SHWFS with 36 subapertures (d = 10 cm) with a hexagonal arrangement and a 35 element
bimorph mirror. The FOV of the subaperture images is 12” × 12” sampled with 24 × 24 pixels.
Using more pixels per subaperture increases the tracking stability (Berkefeld, 2007). Significant
effort has been spent to automate many system calibration functions, which is essential for
making the system operational to the non-expert user and enabling remote system support.
The system frame rate was increased in 2006 in order to increase the system bandwidth to
approximately 100 Hz. The minimum seeing needed to achieve diffraction limited observations
is 0.8”. The processor unit is a general purpose Sun Fire V880. Figure 34 shows the optical
implementation of KAOS into the German VTT on Tenerife. Figure 35 (left) shows quantitatively
what level of correction can be achieved with KAOS as a function of the Fried parameter. The
uncorrected and corrected power spectral density is plotted as well in Figure 35 (right) and indicates
that a bandwidth of about 100 Hz is achieved. The residual rms wavefront error is 0.1 waves
and a Strehl of S = 0.7 is achieved for seeing of about r0 = 20 cm. In comparison, the high
order DST AO76 system achieves a Strehl of S = 0.7 for seeing of r0 = 8 cm. Figures 36
and 37 show uncorrected and corrected granulation movies, respectively, that demonstrate the
ability of KAOS to compensate for atmospheric turbulence and fixed aberrations of the optical
Figure 34: Opto-mechanical implementation of KAOS at the VTT on Tenerife (from Rimmele,
Figure 35: Performance of KAOS. Left: Residual wavefront errors are plotted vs. the Fried
parameter r0 (from Berkefeld, 2007). Right: Corrected and un-corrected temporal PSD of wavefront
errors. The crossover occurs at a bandwidth of about 100 Hz (from Berkefeld et al., 2007).