Aidan was in Hanford this week, so I switched gears and worked mostly on modematching the 35W PSL with Dmass. This requires passing the beam through a couple of lenses to alter the waist size and location before it enters the PMC. Last year, he took some beamscans postlenses. We wanted to see if this data matched with the prelens beam parameter. I used ray transfer matrices to perform the inverse calculation. We found a mismatch between the calculated and expected waist location, which could not be fully explained by the engineering tolerance of the lenses or by the lens orientation.
Dmass also noticed something funny about the head of one of the lenses, so he made some changes to that and made more beamscans that we will look at.
There are a number of objectives for the upcoming week:
1) We believe that the 1W NPRO is elliptically polarized. I learned about Jones vectors and Jones matrices, which are a convenient linearalgebraic representation of a beam's polarization and how it changes as it passes through various optics. The beam can be linearly polarized by passing it through a quarterwaveplate (QWP) whose fast axis is correctly angled. To test this, I will pass the beam through a QWP, and aligned a halfwaveplate (HWP) and polarizing beamsplitter (PBS) to find its extinction ratio for various QWP angles. (The extinction ratio is the ratio of the minimum to maximum transmitted powers of the beam as the HWP is rotated.)
2) I'll work on coupling the 1W NPRO into a 50m fiber.
3)I'll align a MachZehnder interferometer to measure the phase noise of the 1W NPRO, and also single pass the beam in one arm through the 50m fiber and characterize the phase noise it acquires.
