Gradient 9

The Gradient 9 surface may be used to model SELFOC ® materials available from NSG America, Inc., or any gradient glass with a similar index variation. The shape of the Gradient 9 surface is the same as the Standard surface plus a "tilt" term in both x and y directions:

where c is the curvature (the reciprocal of the radius), r is the radial coordinate in lens units, k is the conic constant, and tan α and tan β are the tangents of the tilt angles in x and y. Note this is not the same surface shape as a tilted Standard surface, but it is a close approximation as long as the curvature is small, or if the tilt angles are small. The Gradient 9 surface has the following gradient profile:

Both A and n0 are functions of wavelength:

where the wavelength is measured in micrometers. The dispersion data is user defined and is stored in an ASCII file called GRADIENT_9.DAT. This file is stored in the folder <glass> (see "Folders"). The GRADIENT_9.DAT file contains blocks of 6 lines each. The first line in the file is the name of the material, which can be any name (without special characters such as spaces or quotes) less than 20 characters long. The next 5 lines are the values for B, C, K0, K1, and K2. There are no blank lines allowed between blocks. OpticStudio can read in data for up to 25 different materials in the GRADIENT_9.DAT file.

The dispersion data in the supplied GRADIENT_9.DAT file was provided by NSG America, Inc., in Somerset, NJ, (732) 469-9650, or by Corning, Inc., Corning NY, (607) 974-4755. Contact the respective manufacturers for detailed information on material properties. Not all of the materials offered by these manufacturers are necessarily included in the GRADIENT_9.DAT file. The included materials are: SLS-1.0, SLS-2.0, SLW-1.0, SLW-1.8, SLW-2.0, SLW-3.0, SLW-4.0, and SLH-1.8 for NSG and Corning-Grin for Corning.

To use the Gradient 9 surface materials, change the surface type to Gradient 9, and then enter the appropriate material name in the glass column of the Lens Data Editor.

The maximum step size Δt determines the trade-off between ray tracing speed and accuracy. For details see "Discussion on maximum step size for GRIN surfaces". Also see "Restrictions on surfaces following GRIN surfaces".

PARAMETER DEFINITIONS FOR GRADIENT 9 SURFACES

Parameter # Definition
1 Δt
2 tan α
3 tan β

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