Today,

I installed the Tilt sensing optical lever and placed the components of the length sensing OPLEV without the LEN QPD because it was not available. Please see srmoplevupper.jpg for the current setup.

Varies distances from components are listed below:

TM to upper viewport: 990 mm (from CAD)

Upper viewport to steering mirror: 300 mm

Steering mirror to tilt QPD: 157 mm

Steering mirror to beam splitter: 50 mm

Beam splitter to lens 40 mm

Lens to folding mirror: 110 mm

From these parameters, the position of the LEN QPD is calculated to be 383 mm from the lens hence 273 mm from the folding mirror.

The optical lever is on the front side of the mirror, as opposed to the back side which is the case for SR2 and SR3, a change in positive pitch would appear to be a change in positive vertical displacement as seen from the QPD frame. So, I changed the OL2EUL matrix from the MEDM screen so the sign of the calibration factor (obtain later) can be neglected (see srmtmoplevtileol2eul.png). Another thing to note is that the SUM appeared in the MEDM screen is only around 4000 which is one order of magnitude smaller than those for other QPDs from other Type B suspensions.