Aidan.

I removed the LEXAN cover to help locate the conjugate plane of the HWS by the ITM. This test was performed in the following way:

1. Removed Hartmann plate from CCD to get a simple capture of the return beam

2. Added a 50mHz, 4 micro-radian amplitude oscillation to ITMX YAW

3. Captured a series of 100 frames on the HWS, running at 1Hz. Measured the centroid of the overall intensity pattern for each frame.

4. Plotted the centroid vs time. 

5. Determined the <pk-pk> size of the oscillation in the centroid in pixels.

6. Determined the conjugate plane of the HWS near the ITM (or conversely, the conjugate plane of the ITM near the HWS).

<pk-pk>*magnification_of_HWS_optics*pixel_size = oscillation size near the ITM

The goal was to move the HWS along the optical axis until the <pk-pk> size was minimized.

The best I could do was:

<pk-pk> = 0.2 pixels

M = 17.5x

pxiel_size = 12E-6m

Therefore the oscillation size (peak to peak) by the ITM is 42 microns. The peak-to-peak angular change is 16 micro-radians for the reflected HWS beam. Therefore:

the HWS is within 2.6m of the conjugate plane of the ITM.

7. The last step was to replace the Hartmann plate on the sensor and move it an additional 10mm along the optical axis. (The Hartmann plate is mounted 10mm in front of the CCD and this action places the conjuate plane on the Hartmann plate rather than on the CCD).