We show an anomalous behavior in a diffractive lens in which the spot size at the focus reaches a minimum at a numerical aperture of ~0.5 and then increases significantly at higher values. Theoretical and experimental results are presented, along with a comparison with refractive aplanatic lenses, in which the anomaly does not appear to exist.
© 2000 Optical Society of America
Ram Oron, Jacob L. Guedalia, Nir Davidson, Asher A. Friesem, and Erez Hasman, "Anomaly in a high-numerical-aperture diffractive focusing lens," Opt. Lett. 25, 439-441 (2000)