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- How to use TEZI to Tolerance for Manufacturing-Related Surface Sag Error
How to use TEZI to Tolerance for Manufacturing-Related Surface Sag Error
- By Nam-Hyong Kim
- Published 30 November 2005
- Surface Tolerances
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Running the MC analysis
Open the tolerancing window under Tools > Tolerancing > Tolerancing and set set the following values.
Run the tolerancing by clicking OK.
The tolerance reports shows the statistical results for the criteria; RMS wavefront error.
To see the saved monte carlo file, (we only saved one, but we could have saved all of them), open the file named MC_T0001.ZMX located in the same directory as the TEZI.ZMX lens file.
Notice how in the Lens Data Editor the surface #2 type is set to Zernike Standard Sag surface.
Open the Surface Sag analysis under Analysis > Surface > Surface Sag and select surface #2.
If we re-run the tolerance with the Max# parameter set to 27 you would get a sag similar to shown below. Notice how there are more bumps across the surface. The number of Zernike terms can control the frequency of the peaks and valleys (bumps).
Now this is an important point. As we polish a surface from l/5 to l/10 to l/20 to l/50, the RMS surface deviation decreases, but usually the spatial frequency of the irregularity increases. Surfaces polished to say l/5 are often quite "slow" in terms of the spatial frequency of the irregularity, whereas super-polished surfaces often have a very high spatial freqeuncy of irregularity. The optical perfromance of a surface depends not only on the RMS amplitude of the irregularity but also on the frequency of those peaks and valleys, because it is the slope of the surface that bends rays. To illustrate this, open the attached "periodic surface.ZMX" file. The surface #2 type is Periodic with a periodic structure in Y direction only. The 3D layout shows the difference in the ray trace results when the frequency of the periodic structure is increased while keeping the amplitude constant.
The Universal plot shows how the RMS spot size in Y direction changes as a function of the structure frequency.
This is why it is important to model the spatial frequency of the irregularity, as well as its RMS amplitude. See Reference 1 for more details.
Run the tolerancing by clicking OK.
The tolerance reports shows the statistical results for the criteria; RMS wavefront error.
To see the saved monte carlo file, (we only saved one, but we could have saved all of them), open the file named MC_T0001.ZMX located in the same directory as the TEZI.ZMX lens file.
Notice how in the Lens Data Editor the surface #2 type is set to Zernike Standard Sag surface.
Open the Surface Sag analysis under Analysis > Surface > Surface Sag and select surface #2.
If we re-run the tolerance with the Max# parameter set to 27 you would get a sag similar to shown below. Notice how there are more bumps across the surface. The number of Zernike terms can control the frequency of the peaks and valleys (bumps).
Now this is an important point. As we polish a surface from l/5 to l/10 to l/20 to l/50, the RMS surface deviation decreases, but usually the spatial frequency of the irregularity increases. Surfaces polished to say l/5 are often quite "slow" in terms of the spatial frequency of the irregularity, whereas super-polished surfaces often have a very high spatial freqeuncy of irregularity. The optical perfromance of a surface depends not only on the RMS amplitude of the irregularity but also on the frequency of those peaks and valleys, because it is the slope of the surface that bends rays. To illustrate this, open the attached "periodic surface.ZMX" file. The surface #2 type is Periodic with a periodic structure in Y direction only. The 3D layout shows the difference in the ray trace results when the frequency of the periodic structure is increased while keeping the amplitude constant.
The Universal plot shows how the RMS spot size in Y direction changes as a function of the structure frequency.
This is why it is important to model the spatial frequency of the irregularity, as well as its RMS amplitude. See Reference 1 for more details.