ISOB: Tolerance on total P-V irregularity

Operand behavior

During tolerancing, this operand adds sag to the target surface using a Zernike Standard Sag surface, which is added as a Composite Add-on surface. The added sag follows the Zernike Standard Sag equation, with c=k=αi=0, Zernike polynomials 5-37, and to remove piston:

Apertures

If the target surface has a circular off-axis aperture, the Zernike Standard Sag surface will be positioned at the vertex of the off-axis surface by adjusting the tilt and decenter in the Composite property. The Clear Semi-diameter of the new surface is set to the aperture semi-diameter of the target surface, or to the Clear Semi-diameter if no aperture is present on the target surface. Apertures other than circular are not supported at this time.

Inputs

Inputs for the operand are: Surf, Units, Statistics, Nominal, Min and Max.

Surf: The row number in the Lens Data Editor of the target surface.

Units: Choice of units of the Max value. 0 = units of nanometers and is currently the only option.

Statistics: 0 = Always use the Max value for P-V irregularity during Monte Carlo analysis, 1 = Choose the P-V irregularity value from a Gaussian distribution.

Nominal: The nominal value is always 0 for this operand, indicating no added irregularity.

Min: Specifies the lowest added power term and is always set to -Max.

Max: Specifies the maximum irregularity to be added to the surface.

Sensitivity Analysis

During sensitivity analysis, the effect on the Criterion is evaluated for two cases of P-V irregularity: -Max and +Max.

MonteCarlo analysis

For a Monte Carlo analysis, a random value for P-V irregularity between 0 and Max is selected from a Gaussian distribution with a mean of Max/2, a standard deviation of σ=Max/8, and truncated below 0 and above Max.

Correlation of ISOB with ISOC:

If ISOC is also applied to the target surface, the ISOB and ISOC can be correlated so that B (total P-V irregularity) and C (P-V rotationnally symmetric irregularity) are simultaneously satisfied. When correlated, the Zernike Standard Sag surface for the ISOB operand will have rotationally symmetric terms set to zero:. See ISOC for further discussion.

• ISOB may not be applied multiple times to the same surface and will trigger an error.
• If used with ISOC, the preferred order in the TDE is: ISOC, ISOB, and then ISOA. See discussion for the ISOC operand.
• Note that we have removed the piston term from the irregularity, so that a ray falling at the aperture vertex will remain unchanged and not acquire any phase.
• ISOB should not be used with other operands that adjust surface irregularity, such as TEZI, TEXI, or TIRR.
• ISOB should not be used with ISOD; two irregularity surfaces would be added to the target surface if both operands are present.
• Per ISO-10110, power and tilt should be removed from the total perturbation added to the target system, but for speed, the terms are not removed from the ISOB Zernike Standard Sag surface. Some random combinations of Zernike terms may have enough residual power or tilt to affect the results, making the system seem more sensitive to irregularity than it would otherwise be.