Ray-tracing Diagnostics


09/06/01
Current (final?) report on condensing mirror template verification.

After an extended series of measurements of the Viper/SPARO template, the conclusion (as best we can discern, as discussed here) is that the Viper/SPARO template matches the predefined setup of the optical system as defined in the Beam4 ray tracing program.

The following Beam4 ray trace file was used:

6 rays      sparo.ray
  Y0      X0     Z0   @wave
------:--------:----:-------:
 0.000:1.300000:-1.0:       B
 0.000:1.000000:-1.0:       :
 0.000:1.600000:-1.0:       :
-0.350:1.300000:-1.0:       :
-0.350:1.300000:-1.0:       :
0.0000:1.350000:-1.0:       G
Additional columns were used to glean output data from the ray trace, however these four columns were the only input data.

The configureation file used in the raytracing of SPARO is the following:

                                  sparo.opt
    Z        X       Y      C         S     Mir/Len   T       P       R 
--------:---------:-----:--------:---------:-------:-----:---------:-----:----:
   1.5  :   0.0   : 0.0 :-.333333:.01020408: mirror: 0.0 :   0.0   : 0.0 :    :
  -0.5  :   0.0   : 0.0 : 1.1429 :.41699219: mirror: 0.0 :   0.0   : 0.0 :    :
-.00273 :-0.07317 : 0.0 :  0.0   :   0.0   : mirror: 0.0 :   0.0   : 0.0 :    :
-.589941:-1.148669: 0.0 :1.023577:-1.30073 : mirror: 0.0 :92.935396: 0.0 :    :
-.60982 :-0.76102 : 0.0 :  0.0   :   0.0   : detect: 0.0 :-36.51063: 0.0 :    :
        :         :     :        :         :       :     :         :     :    :
        :         :     :        :         :       :     :         :     :    ;
This is the same information used in the report from October, 2000.

The measurements involved used the transformations defined in the report on the coordinate systems as the 'Chopper Coordinate System' (CCS). Briefly, CCS defines the x-axis as a line parallel to the chopper, going through the prime focus spot on the template (a small drilled hole), while the y-axis is perpendicular to the x-axis, travelling through the prime focus spot, which serves as the origin. A total of 185 points were measured on the three available surfaces (65 secondary, 60 chopper, and 60 condensing mirror points), then rotated to the Beam4 coordinate system. Selected points were then plotted in Beam4, and measurements made to determine the distance from the plotted point to the nearest area of the surface.

The results are as follows:

Secondary:

Average difference: .821 mm
Max difference: .9972 mm
Min difference: .443 mm

Chopper:

The chopper was really too close to measure with paper and ruler: I would guess .1-.2 mm.

Condensing mirror:

Avg. difference: 3.21 mm
Max difference: 3.546 mm
Min difference: 2.54 mm

As one would expect if the translations are correct, the chopper lines up exactly, and is very close. The condensing mirror is, however, quite different. However, the points are uniformly shifted by ~3.2 mm in the positive y direction. Thus, if the entire set of points is shifted down, along the direction chopper (since the chopper points are lined up already), the entire set of points (chopper, secondary, and condensing mirror) lines up with the Beam4 settings.

Thus, do to the uncertainty about the correlation of the prime focus hole on the template and the Beam4 file, we conclude that the template is as correct to within our testable limits.


Last updated September 04, 2001 by C. Greer.