Wavefront sensor with Fresnel zone plates for use in an undergraduate laboratory

We propose a modification of the Shack-Hartmann wavefront sensor in which the lens array is made of Fresnel zone plates. The modification allows students to construct the sensor in an undergraduate laboratory at little cost. In spite of its simplicity the sensor has a sensitivity of lambda/50 in relative measurements, which is sufficient to measure a wavefront of a laser beam distorted by various optical elements as well as by a turbulent airflow. Such an experiment is an excellent supplement to a course in optics, gives students a deeper understanding of the wavefront concept, and demonstrates the wavefront measurement technique widely used in physics, astronomy, and medicine. (c) 2008 American Association of Physics Teachers.