Summary:

Elli and Nutsinee measured the current state of the ETMX HWS layout and the behaviour of a beam transmitted through it. From this I was able to solve for unknown distances in the layout and produce a new optical solution that will image the ETM onto the HWS with the existing lenses.

Diagnosis:

Elli and Nutsinee made some measurements of the ETMX HWS yesterday to determine the conjugate plane. We started with the following measurements:

• lens L1 focal length = 2.2361m, [CVI PLCX-50.8-1030.2-UV-532]
• lens L2 focal length = 2.2361m, [CVI PLCX-25.4-1030.2-UV-532]
• lens L3 focal length = -0.5589, [CVI PLCC-25.4-257.2-UV-532]
• L1-L2 distance = 610mm
• L2-L3 distance = 928mm
• L3-HWS distance = 1401mm

Also, we know the following measurements of the transmon telescope (Data from T0900385 - v06 and G1100873):

• ETM to Transmon Primary Mirror = 1429 mm
• Primary Mirror ROC = 4000 mm
• Primary to Secondary Distance = 1902.6 mm
• Secondary ROC = -200 mm
• (Nominal) Secondary mirror to HWS Lens L1 = 5273 mm (this one is the problem).

This list of values allows us to calculate the ABCD matrix propagating the beam from the ETM to the HWS.

Elli and Nutsinee injected a 2 urad oscillation into ETMX YAW at 0.05Hz. This results in a peak-to-peak oscillation of 8 urad on the reflected beam (pk-pk multiples by a factor of 2, reflection multiplies by another factor of 2). They then measured the pk-pk oscillation of the centroid of the return beam on the HWS in pixels, where 1 pixel = 12 um, for different positions on the HWS. At the conjugate plane, this should be zero.

• For L3-HWS = 1401mm, centroid oscillation = 7.629 pixel pk-pk
• For L3-HWS = 1351mm, centroid oscillation = 6.648 pixel pk-pk

These numbers didn't jive with the nominal optical layout. The only real uncertainty was the distance "Secondary mirror to HWS Lens L1". So, using the values that for the oscillations, I readjusted this value in the ABCD matrix, modeled the expected centroid oscillations and compared the measured oscillations.  "Secondary mirror to HWS Lens L1" = 5728mm gave a result that agreed to better than 1%. 

New Optical Solution:

So now that we "know" the values for all distances, I re-solved for an optical solution that would image the ETM onto the HWS with a demagnification of -20.5x with the existing lenses. The new values are:

• L1 to L2 = 610 mm
• L2 to L3 = 877 mm
• L3 to HWS = 1499 mm

The calculations are attached.

Diagnosis calculation

New solution calculation

XorYDist = (nominal) + (unknownX) = 5.273m + 0.455m