The actuator layout of 19- and 18-channel PDM has been especially developped for correction of the low-order abberrations (see  for the theoretical background). In 18-channel version, the central actuator is absent (see Fig.1), and thus all actuators are outside the 20-mm active aperture. Although this makes impossible generation of any aberration containing Zernike terms other than , e.g. spherical aberration, the mirror benefits from the increased range of the defocus amplitude and more accurate generation of the other aberration.
Here, we present the results of generating of the first Zernike modes with 30-mm version of 19-channel PDM, obtained in a closed-loop system operated by FrontSurfer. With the rms error growing linearly with the amplitude of an aberration, the amplitude of the presented aberrations corresponds to 0.1µm rms error.
[ 1] Gleb Vdovin, Oleg Soloviev, Alexander Samokhin, and Mikhail Loktev. Correction of low order aberrations using continuous deformable mirrors. Opt. Express, 16(5):2859-2866, 2008.