OP: Ruben Biesheuvel started his MSc project
Ruben has started his MSc project which focusses on testing different algorithms of retrieving the Zernike Polynomial coefficients that describes a certain wavefront. This is a joint project between the Optics group and the CSI2 group of the DCSC (3mE), with Silvania Pereira and Paolo Pozzi as supervisors.
A Shack-Hartmann sensor is widely used to measure the wavefront, but rather than directly measuring it, the Shack-Hartmann sensor is only able to measure the derivatives. For this reason, reconstruction can be troublesome for a quickly varying wavefront. Janssen has found an analytical relation between the slope of the wavefront and Zernike Coefficients to describe the wavefront. The hypothesis is that this method could be more accurate for quickly varying wavefronts.
In order to test the accuracy, an adaptive optics setup is built. In the beginning of the project, a deformable membrane mirror will be used in order to introduce specific aberrations in the wavefront, and these aberrations will be measured using the Shack-Hartmann sensor and independently with an interferometer. The algorithms that will be tested are a well-known Least Squares method, an iterative integration method and Janssen’s method. If successful, a spatial light modulator will be used in order to create more extreme cases of quickly varying wavefronts.
 Janssen, A. J. E. M. "Zernike expansion of derivatives and Laplacians of the Zernike circle polynomials." JOSA A 31.7 (2014): 1604-1613.