Shack–Hartmann multiple spots with diffractive lenses

In this Letter we aim to bring an understanding to the apparition of multiple spots when using a Shack–Hartmann (SH) wavefront sensor behind diffractive lenses. In contrast to previous work, this phenomenon is described in terms of diffractive orders. It is illustrated with Zemax simulations, where three kinds of diffractive lenses (mono-focal, bifocal, and trifocal) are set behind a microlens array. The presence of multiple spots is related to the phase jump of the diffractive profile and also to the number of steps seen through the microlens pupil. The possibility of assessing the optical quality of such lenses using SH measurements is discussed, in particular within the field of ophthalmology, where the need for precautions is underlined. © 2011 Optical Society of America OCIS codes: 050.1965, 170.4470, 040.1240. When measuring diffractive lenses behind a Shack– Hartmann (SH) wavefront sensor, it has been shown that multiple spots can appear [1–3]. Physically misunder-standing that effect can lead to wrong conclusions about the optical quality of such lenses. This is particularly true in ophthalmology, for example, for patients with diffrac-tive intraocular implants after operations for catarac