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