GRIN Lens
The GRIN lens is a plane-parallel slab of material with a quadratic transverse variation of refractive index, with either a maximum or minimum on the axis that produces a lensing effect. The element has similar matrices for both work planes, but gradient constants n2 can be set independently for tangential and sagittal planes.
Note that this element represents a piece of GRIN-medium in free space. It has planar input and output interfaces. If you want to build a more complex GRIN-rod, e.g., having one or both curved interfaces, you should use the GRIN Medium element and surround it with appropriate interface elements.
Full element
Beam propagation inside the lens also can be calculated.
Left half-pass
Right half-pass
When the gradient constant n2 is set to zero, the element becomes simple Plate of Matter.
See also
GRIN Medium, Elements Matrices, ../catalog, ../elem_props, Gradient-index optics in Wikipedia