
Energy acceptance meritoid
The energy acceptance meritoid calculates the energy fraction captured from an isotropic point source by a lens feeding a fiber optic of a specified numerical aperture. The fiber optic is at the image plane. This is a purely geometrical calculation, and does not take into account energy losses in the lens due to reflections, scattering, or absorption. An aperture should be placed on the image plane if the finite spatial extent of the fiber is to be included.
Set the cutoff parameter to the acceptance NA of the fiber.
This meritoid is an "inverting meritoid". It contributes a reciprocal residual to the merit function. Optimization aims to minimize this reciprocal residual, which maximizes the value of the meritoid.
Parameters
- Field coordinates
- The quantities Hx and Hy are the reduced field coordinates (between -1 and 1) specifying the position of the point source on the object in the case of finite object distance or the direction to the point source in the case of infinite object distance.
- Wavelength
- You can use the arrow to pick from any of the defined wavelengths or you can enter your own value. The wavelength is specified in nanometers (nm).
- Search
- Using the Search popup menu, select the method used when searching for the boundary of the pupil. Presently the only option is "Spherical octahedron" for a finite conjugate system or "Hexagon" for an infinite conjugate system. The "Spherical octahedron" option uses a recursive spherical triangulation, starting from a spherical octahedron, to search the entire forward half of the emission sphere of an isotropic emitter to determine the solid angle into which emitted energy must pass in order to reach the indicated surface. The "Hexagon" option uses a recursive planar triangulation in the input plane, starting from a hexagon, to find the area through which emitted energy must pass in order to reach the indicated surface.
- Depth
- During the search for the boundary of the pupil, triangles are subdivided where they straddle the boundary between captured and lost energy. The recursion depth parameter is the number of subdivisions. Typically 7 will yield a good result.
- Min
- Before the search, triangles are subdivided to this depth before testing for ray capture. This increases the resolution of the search in the interior of the pupil, but at the cost of much additional ray tracing. Usually this parameter can be left at zero.
- Cutoff
- Value and quantity to use to determine if rays are accepted or not. Presently the only option is the so-called "transverse momentum" which is the product of the image space index of refraction and the sine of the angle between the ray direction and the image surface normal. In other words, the "numerical aperture" of the fiber optic.
- Present value and aperture
- How to display the accepted energy fraction. Transforms the raw data to various representations. For finite conjugate system, the options are solid angle, fraction of sphere, fraction of hemisphere, or numerical aperture.
- Target
- The target is specified in the same units as the displayed value. If the target is zero (the usual case) the meritoid is multi-residual as described above.
- Tolerance
- The tolerance is specified in the same units as the displayed value and specified target. Using this tolerance a dimensionless residual is created in the usual way.