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User name X. Zheng
Log entry time 16:16:22 on June14,2001
Entry number 63082
keyword=Laser power and waveplates check
It has been found that the target polarization drops after we turned on the 4th longitudinal laser.
First I checked power of Coherent #5, at operation current 36500mA it is 30.1 W.
Next, I switched fibers for Coherent #4 and#5. Now Coherent #4 is used for fiber/laser #5 and Coherent #5 is for fiber/laser #4. This is because the spectrum of Coherent #5 has not been tested so we put it at fiber/laser #4 which has the worst alignment.
Last thing I did is:
I checked the orientation of quater waveplates for all lasers. Slow/fast axies' direction of all quater waveplates have been tested in the lab. We defined an angle "THETA" which means when the waveplate mount reads "THETA" the slow axis is positioned at the horizontal direction.
During laser alignment the left & right quater waveplates are all set to be (THETA + 135 degrees), which should give left-handed polarized light (this has been tested by EPR resonance frequency, both in lab and in the hall). Quater wavplate #4 and #19 are used for the 4th longitudinal laser (laser #4), one suspicious thing is that I found the THETA of #19 written in the laser logbook was the only one which has been crossed out and corrected. This correction means I had some confusion when I tested it in the lab, so THETA of #19 might be wrong (by 90 degrees).
To make things more reliable I switched quater waveplate #19 (originaly laser #4, left) and quater waveplate #21 (originally for excitation of laser #4), since the orientation of excitation quater waveplate doesnot depend on slow/fast.
In more details:
quater waveplate #: 4 || 19 || 21
THETA in logbook: 35 || 115 || 78 (degrees)
original used for: right || left || excitation - of laser #4
original setting: 170 || 250 || 123
currently used for: right || excitation || left - of laser #4
current setting: 170 || 160 || 213