I want to create an axicon in OSLO. Is there a surface type that does this? How do I go about using it?
Synopsis
Creating an axicon in OSLO
Solution
"The word
axicon is typically used to describe a cone-shaped surface that is symmetrical about an axis of revolution (the local z-axis). An axicon typically focuses light into a ring shape.
The sag equation for the surface (the deviation from a flat plane), is defined as
The surface can be represented in OSLO in two ways:
Using the linear term of the odd polynomial Symmetric Asphere (all orders) [available in Light, Standard and Premium]
Using the appropriate conic constant in combination with a very small radius of curvature [available in all editions of OSLO]
Approach #2 is preferred because this approach does not have a surface discontinuity when
r = zero (at the nose of the axicon). Additionally, the small radius of the surface mimics how the axicon most likely would be built (with a very small, but non-zero radius at the nose of the axicon). The conic constant (k) can be defined as a function of the desired angle (theta):
Note that the surface will be defined with a non-linear "transition" region between the radius of curvature and the true cone section nearer to the outer region of the surface aperture. For this reason, the surface radius of curvature should be many times smaller than the closest rays to the axicon axis or these rays will not experience a true linear cone surface. You can make the radius of curvature extremely small (even less than a wavelength), but do not make it zero.
