Axially translating aspheric phase plates generate varying amounts of spherical aberration -- or of conical wavefront

Tucson, AZ and Santiago de Compostela, Spain--Optics researchers José Sasián of the University of Arizona and Eva Acosta of Universidad de Santiago de Compostela have developed a new way of introducing user-variable amounts of fourth-order spherical aberration into an optical system; a second version of the device also can be used to introduce user-variable amounts of conical wavefront (the same type of wavefront produced by an axicon lens).¹ Other versions are also possible.

The optical device consists of two axially placed, rotationally symmetric elements (phase plates), appearing roughly like a plano-convex and a plano-concave lens with the curved surfaces facing each other with a small gap between them. However, the inner surfaces are highly aspheric and the outer surfaces may have a slight curvature also.

Relative axial displacement
The system operates on the principle of "extrinsic aberrations," or the introduction of additional aberrations into an already aberrated (rather than nonaberrated) beam by an element that contributes aberration. The axial spacing between the elements is varied to vary the amount of introduced spherical aberration (or conical wavefront). Previous setups have been designed where two nonrotationally symmetric phase plates are either laterally translated or rotated with respect to each other, but the new device relies on a relative axial displacement instead, as well as simpler optics.

The device could be useful for tweaking out aberrations in an optical system or, in the case of the conical-wavefront device, as a tweaker in various axicon-related systems such as optical tweezers or Bessel-beam-producing optics.

REFERENCE:

1. Jose Sasian and Eva Acosta, Optics Express (2014); doi: 10.1364/OE.22.000289