Aberration-free imaging with an aplanatic curved diffractive element.

We demonstrate an imaging diffractive optical element (DOE) that is free of coma and other first-order aberrations. The DOE was holographically recorded on a properly curved surface and thereby satisfies the Abbe sine (aplanatic) condition. Experimental results as well as numerical ray-tracing simulations indicate that the off-axis aberrations of the curved DOE are much smaller than those of a flat DOE. Because the recording of the DOE involves a single step and only readily available spherical and plane waves, it is extremely simple.