[1] This wavefront sensor uses a pyramidal prism with a large apex angle to split the beam into multiple parts at the geometric focus of a lens.
A four-faceted prism, with its tip centered at the peak of the point spread function, will generate four identical pupil images in the absence of optical aberrations.
The local wavefront gradients can be obtained by recording the distribution of intensity in the pupil images.
This makes the wavefront sensor slightly inconvenient to use due to the need for mechanically moving parts – either the prism or the beam is modulated.
[4] Alternatively, it has been shown that the need for mechanically moving parts can be overcome in a digital pyramid wavefront sensor with the spatial light modulator.