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Wavefront sensor is a device that measures the optical wavefront aberration. The Shack Hartmann wavefront sensor (SHWS), named after Johannes Franz Hartmann and Roland Shack, is one of the most often used optical wavefront sensor. It is made up of an array of microlenses (all having the same focal length and aperture size) and a detector placed at the focal plane of these microlenses. Johannes Franz Hartmann developed a device that consisted of an opaque screen with multiple holes to test the quality of imaging in large telescope systems and fine-tune the telescope focus (Hartmann, 1900). In the process of developing an adaptive optics system to improve the resolution of satellite images taken from the earth, Roland Shack came up with a feasible model of the sensor by using an array of tiny lenses instead of holes (Shack & Platt, 1971). The technological advancements in the field of optical fabrication allowed the industry to make lenses as small as 100 μm using materials like fused silica, ZnS, ZnSe, Si, Ge, etc. Individual microlenses are also called subapertures and the SHWS spots formed at the focal plane where the detector is placed are referred to as “spots” in this chapter.

Advanced Methods for Improving the Efficiency of a Shack Hartmann Wavefront Sensor