Kiwamu, Sheila

This morning Kiwamu and I went into the PSL to see if we could improve the coupling of the reference cavity transmission into the ALS fiber.  There were 4.72mW of light incident on the fiber coupler. We connected the two ends of the fiber at the field rack to each other so that the light was returning to the PSL with some extra losses due to the extra coupler, and saw 1.46mW coming out of the fiber.  We moved the lens closer to the fiber coupler closer to the fiber coupler by about 1 cm total, and saw the power on our power meter inside the PSL increase to 2.1 mW. We noticed that as we moved the lens the alignment changes not only in yaw but also in pitch, meaning that the beam is not centered vertically on the lens.  We can probably improve the coupling more by adjusting the lens positions more, but this will be easier to do if we have a beam leveler and make sure the beam is really level before we start.  

When we left Kiwamu measured the power coming out of the fiber at the rack, which was 2.4mW, so now the coupling efficiency is 51%.  Better than 37% measured yesterday but there is still room to improve.