Repeat yesterday's scan with the filters taped to the front of the DCOPS, to avoid any tipping distortions.
To repeat: each of the cross-hair lasers is an ordinary laser pointer type of laser which is directed into a cylindrical lens to turn the narrow laser beam into a beam fan. We have a DCOPS mounted on a plate that lets us adjust the horizontal position using a screw. I start with the plate at one end of the mount and move it equal increments, taking fresh readings each time, until I reach the end of the travel. Two polarizing filters are taped in front of the DCOPS, which has vector away from the laser (CCD2 and CCD4 are closest to the laser), which is 127mm away from the entrance to the CCD holder.
I plot both CCD2 and CCD4 together below. The distortion is still plainly present, and is clearly not due to screw mechanism problems.
Next I rotated the laser mount to scan what used to be the vertical laser fan.
I plot the variation of CCD2 and CCD4 together below. There is fairly severe distortion once you get past 8 degrees from the center of the laser fan. Note that this is a different laser. It looks worse than the other one in the set, but this may be an illusion. I need to subtract out the central region's slope.
When I subtract off the central slopes, the curves look very similar (although the green vertical ones are inverted wrt the black horizontal laser curves).
Scan the other two lasers in the spare set we have.
Center the DCOPS on the crosshair and move it along the crosshair line from approximately the position of the reference sensor to the position of the first chamber sensor.
Somehow we need to check the transfer line lasers.
Modified 01-May-2009 at 13:50
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