GMT Principal Test

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Index:

  1. The telescope

  2. Primary mirror segment

  3. Design of null test

  4. Tolerance analysis

  5. Alignment plan

  6. Prototypes

The Telescope:

Giant Magellen Telescope

System

An Off-Axis Segment

　

The Off-Axis Segment of Primary Mirror:

Parameter Value
Parent ROC at vertex 36 m
Parent conic constant -0.998286
Off-axis distance 8.71 m
Diameter 8.4 m
Zemax file GMT Mirror.zmx

　

Design of Null Test:

The principal test is an interferometric null test. The null lens consists of a big fold sphere (3.75m in diameter), a small fold sphere (0.75m in diameter) and a CGH. The test layout is shown below:

　

Zemax files

Data files

System design and analysis

Test CGH

Reference CGH

Reference CGH

　

Alignment Tolerance Analysis:

File No. Remark
1
For each degree of freedom:
  • •Simulate perturbation of test optics
  • •Simulate optimization in telescope using mirror radial position, clocking
  • •Simulate bending
  • •Evaluate residual wavefront
Combine effects of all degrees of freedom using RSS (root sum square)
2 Only difference from above is:

For big fold sphere's ROC error, the COC is fixed so that the fold sphere has a piston due to the ROC error.

　

Alignment Plan:

See here for our preliminary alignment plan.

　

Prototypes:

One of the prototypes we plan to do is the reference CGH assembly which contains the reference CGH with several SMRs and prisms glued on the CGH substrate. We want to see if we can get the reference CGH coordinate into the laser tracker's coordinate system accurately enough for aligning the big fold sphere. Here is our design of the prototype.