Adaptive secondary mirror for the 6.5-m conversion of the Multiple Mirror Telescope: latest laboratory test results of the P36 prototype

The 336-actuator adaptive secondary unit (MMT336) for the new MMT is being assembled in Italy and will be delivered in June 2000 for the acceptance test at Steward Observatory (Tucson, AZ). The latest results obtained on a reduced-size (36 actuators) prototype called P36 are reported, confirming a settling time less than 1 ms measured in previous tests. The flattening procedure has been successfully tested on the P36 unit, reducing the initial surface error of 1.1 micrometer down to 43 nm rms. Moreover the dynamical tests on the P36 unit show that the system is able to attenuate the atmospheric-induced error from 466 nm to 31 nm rms. This in the case of median seeing condition at MMT (0.75 arcsec) a high wind speed (48 m/s) and a 1 kHz command rate per actuator. Finally, in the same conditions the atmospheric error is effectively attenuated up to a frequency of 100 Hz (OdB attenuation level).