Pupil Lens Location

The purpose of this test was to ascertain the best position of the ZnSe lens in the lens wheel.  This test was conducted warm using the red laser and the cold stop wires.  The data can be found in directory /data/Warm017/warm017_2013dec/20/.  The position of the lens was measured from the top of the lens teflon ring to the top of the lens barrel (Delta z, see Figure 1).

Figure 1.

As the position of the lens was moved, the magnification of the pupil image changed.  To account for this difference, the diameter of the pupil was measured for each image and the FWHM was scaled accordingly.  The FWHM was estimated by measuring the FWHM of the two parallel cold stop wires using a 1D gaussian fit.  The two wire values were then averaged to obtain the final value to each pupil image.  The error was estimated solely by repeating the diameter and FWHM measurements 5 times for each pupil image and so should be taken as a lower limit since there are many other possible sources of error.  Figure 2 shows how the FWHM changes with pupil lens location.  From this experiment I do not believe it is possible to conclude that one position in the lens barrel is significantly better than the others and so it may be best to place the lens in the previous cool down location.

Figure 2.