Calendar

Advanced Topics in CODE V April 7-11, 2008
Pasadena, California
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Introduction to CODE V
Sept. 29-Oct. 3, 2008
Pasadena, California
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Advanced Topics in CODE V
October 6-10, 2008
Pasadena, California
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CODE V Tip - Using CODE V's Alignment Feature to Respace a Lens

CODE V's Alignment option (ALI) is primarily intended to determine tilts and decenters of a system that has been built so that adjustments can be made to bring a misaligned system back to its design specifications.  When used in this manner, interferometric measurements of the as-built system are made and imported into the ALI option, which predicts what changes in alignment are needed.   However ORA's Engineering Services have also used the ALI to determine how to respace lenses in a system if their measured radii or thicknesses are known, but do not match the nominal design specification.  Here's how ALI can be used to do this:

• First, make the nominal lens setup monochromatic in the reference wavelength.  This procedure will work if the lens respacings are small enough to not appreciably affect color correction.
  
  
• Use CODE V's Pupil Map option (PMA) to create interferogram files for the nominal lens, with its as-designed air spaces:
  
  
  • In the GUI:
    1. Analysis > Diagnostics > Pupil Map
    2. On Zernike Coefficient Tab, select Standard Zernike and "Fit to exit pupil plane, normal to chief ray"
    3. On the Output Control Tab, enter the name for the exported interferogram
       file (e.g., perturb)
       
       
  • Or, at the Command line:

    PMA; ZRN EXP 36; WIN perturb; GO

  For each field in your system, a separate version of the interferogram file will be created (i.e., perturb.1.int; perturb.2.int, and perturb.int for fields 1, 2, and 3).

• Make necessary changes to create an as-fabricated version of the nominal system by changing lens thicknesses and/or radii to match the manufactured lenses.
  
  
• Designate all adjustable air spaces as tolerance compensators (Lens > Surface Properties > Advanced > Tolerances; or CMP DLT Sk).  Focus should also be a compensator (DLZ SI).   Compensator limits can also be included, and depending on mount structure, Z-axis displacement (DLZ) compensators may be required in place of thickness (DLT) compensators (e.g., DLZ S3..4 will move the element defined at surfaces 3 and 4 within its space without increasing the system's overall length).
  
  
• Run ALI (Analysis > Fabrication Support > Alignment Optimization) with these compensators, using the PMA-created interferograms for each field.
  
  
• Restore the as-fabricated lens.  Using the ALI predicted adjustments, apply the changes in airspaces using the opposite sign output by ALI.
  
  
• Analysis of the modified lens system should show improved performance of the respaced design.  You should also review for possible constraint violations, distortion changes, and chromatic affects since ALI does not provide constraint/distortion control or polychromatic solutions.

Why is this approach sometimes better than doing the respacing using CODE V's optimization (AUT)?  Using ALI has the advantage that it works to match the original wavefront balance over the field and minimize the set of alignment changes.  More importantly, it copes with the problem of having a greatly reduced set of available variables.  Usually, an optimization problem contains numerous constraints and field weights which have to be modified by the user when the list of available variables drops to only select airspaces.  This approach, which minimizes the change in the parameter set, can be a very effective means of maintaining constraints while providing compensation for as-fabricated lens data.

Updates to ORA's Customer Service Web Site

The following additions have been recently made to ORA's Customer Service area of the web, www.oraservice.com, under CODE V Support:

• The March issue of CODE V Enews, which featured an overview CODE V version 9.81, is available under CODE V Enews & Tips.

• Recorded demonstrations of the new features included in CODE V 9.81 are available for viewing under Webinar Recordings.
  
  
• An updated copy of the 2007 presentation "Compensator Selection using Singular Value Decomposition for Tolerancing & Alignment" has been added under User Group Presentations.  The update includes additional examples and explanatory graphics.