Polarized Source -- Improvements and Other
Issues
Ryan Snyder
December 3, 2005
Position Differences from the Pockels cell have two sources
birefringence gradients and steering
And… A good Pockels cell alignment can help to minimize these two factors
Measuring Position Differences
Pockels cell alignment
1. Maximize extinction between crossed LP’s-adjust pitch/yaw to maximize extinction
2. Adjust PC voltages and roll angle to minimize outgoing linear polarization
3. Do pitch/yaw scans (with downstream LP) and make indicated adjustments --> check dx, dy (biref. grad. + phase grad.)
4. Remove LP -->translate PC to minimize dx, dy (steering)
Beam divergence
• Very sensitive to interaction of beam angle with indices of refraction
Hydrogen Setup
DOLP = 99.8 % (upstream)
-- not measured with IHWP IN
With HV ON
--DOLP ~ 4%
--DOCP ~99.93%
Pitch Scan = 7.6 um/turn
Yaw Scan = -20.3 um/turn
After pitch/yaw adjustment,
IHWP OUT
Dx = -0.41 +/- 0.23 um; Dy = -0.65 +/- 0.18 um
But, with IHWP IN
Dx = 3.6 +/- 0.29 um; Dy = 2.3 +/- 0.25 um
A compromise was made…
After pitch and yaw scans with IHWP IN a compromise was made
IHWP IN
Dx = 1.23 +/- 0.18 um; Dy = 0.25 +/-0.23 um
IHWP OUT
Dx = 0.98 +/- 0.18 um; Dy = 0.70 +/- 0.23 um
Steering -- Lever Arm = 88 cmIHWP OUT
Dx = -0.20 +/- 0.17 umDy = -0.17 +/- 0.18 umAq = -190 ppm
IHWP IN
Dx = -0.12 +/- 0.12 umDy = -0.09 +/- 0.13 umAq = +198 ppm
Problems and Other Issues Not Understood on Laser Table
1. Poor Initial Cancellation of Dx and Dy between IHWP IN and OUT
2. Sensitive to Dx with Pitch Scan and Dy with Yaw Scan
3. ~190 ppm Aq that flips sign from IHWP IN to OUT
Helium setup (July on Gun 3)
1. Helicity correlated electronics pickup up to Sept. down -- not related to laser table setup
2. Incoming DOLP = 95 % ==> DOCP = 30% -- 7 extra mirror bounces for Gun 3 compared to Gun 2
3. Pockels Cell alignment was very difficult
4. Large ~750 nm pos. diff. that flips sign with IHWP plate without an analyzer downstream of PC -- Lever Arm = 67 cm
5. More sensitive to pitch in y than x (makes sense); Also, more sensitive to yaw in y than x (doesn’t)
Helium Setup -- July
Helium Setup -- After Sept. Down
Helium since Sept. down
Hydrogen Setup -- Oct. 12th
Drifts over timebpm1I02 -- first bpm after cathode
Oct. 12th Dx = ~0 nm; Dy = 200 nm
Oct. 17th Hall A Laser Lock fix
Nov. 2nd Dx = 600 nm; Dy = ~0 nmNov. 7th Dx = 600 nm; Dy = -150 nm
Nov 8th -- > cathode spot move
Nov. 10th Dx = 550 nm; Dy = -200 nmNov. 17th Dx = 1.2 um; Dy = -800 nm
Pockels Cell OFF Run
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