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Polarized Source -- Improvements and Other Issues

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john
21 diapositives · 333 Views · Aug 14, 2014

Learn how to improve Pockels cell alignment to minimize birefringence gradients and steering issues for enhanced performance. This guide includes step-by-step instructions and key adjustments to maximize alignment accuracy and beam divergence control.

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Polarized Source -- Improvements and Other Issues
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  1. Polarized Source -- Improvements and Other Issues Ryan Snyder December 3, 2005

  2. 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

  3. Measuring Position Differences

  4. Pockels cell alignment • Maximize extinction between crossed LP’s -adjust pitch/yaw to maximize extinction • Adjust PC voltages and roll angle to minimize outgoing linear polarization • Do pitch/yaw scans (with downstream LP) and make indicated adjustments --> check dx, dy (biref. grad. + phase grad.) • Remove LP -->translate PC to minimize dx, dy (steering)

  5. Beam divergence • Very sensitive to interaction of beam angle with indices of refraction

  6. Hydrogen Setup DOLP = 99.8 % (upstream) -- not measured with IHWP IN With HV ON --DOLP ~ 4% --DOCP ~99.93%

  7. Pitch Scan = 7.6 um/turn

  8. Yaw Scan = -20.3 um/turn

  9. 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…

  10. After pitch and yaw scans with IHWP IN a compromise was made IHWP IN Dx = 1.23 +/- 0.18um; Dy = 0.25 +/-0.23 um IHWP OUT Dx = 0.98 +/- 0.18 um; Dy = 0.70 +/- 0.23 um

  11. Steering -- Lever Arm = 88 cm IHWP OUT Dx = -0.20 +/- 0.17 um Dy = -0.17 +/- 0.18 um Aq = -190 ppm IHWP IN Dx = -0.12 +/- 0.12 um Dy = -0.09 +/- 0.13 um Aq = +198 ppm

  12. Problems and Other Issues Not Understood on Laser Table • Poor Initial Cancellation of Dx and Dy between IHWP IN and OUT • Sensitive to Dx with Pitch Scan and Dy with Yaw Scan • ~190 ppm Aq that flips sign from IHWP IN to OUT

  13. Helium setup (July on Gun 3) 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)

  14. Helium Setup -- July

  15. Helium Setup -- After Sept. Down

  16. Helium since Sept. down

  17. Hydrogen Setup -- Oct. 12th

  18. Drifts over time bpm1I02 -- 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 nm Nov. 7th Dx = 600 nm; Dy = -150 nm Nov 8th -- > cathode spot move Nov. 10th Dx = 550 nm; Dy = -200 nm Nov. 17th Dx = 1.2 um; Dy = -800 nm

  19. Pockels Cell OFF Run