Aidan, Daniel V-H., TVo, Dan B., Terra

This is the initial analysis of the HAM6 output beam scan we did last week. Attached is the overall picture, in the style of LLO's beam study.

Measurements are done in HAM6 during single bounce configuration (no TCS) either directly in beam or using pickoff. Data is then fit by varying input beam parameters and, to some degree, OM optical/path length parameters. These are compared against the original output beam design. (There is a caveats to this, see below.) Since there was large astigmatism, what I show is beam fit prioritized to fit vertical measurements. [R,w] directly after SRM for design and vertical fits shown in plot. X-axis distances are in meters from SRM.

Main points:

•  we find up to 20% astigmatism coming into HAM6 
  • Finesse modeling for the single bounce beam parameters using the up-to-date design configuration shows about 3% astigmatism coming out of the SRM
  • table-top check of beam profiler gives 2-3% variation between vertical and horizontal, even when tilting scanner various ways with respect to incoming beam (NanoScan NS-SI/9/5 scanning slit profiler)
• looking at just the vertical beam, fit mismatch from OMC is ~5%
• we find similar shifts in OM placements (towards SRM) as LLO compared to original design; the distance between the edge of the ISI and OM1 & OM1 to OM2 was measured in situ. We find the latter agrees with up-to-date Zemax distance.

Caveat/to do: the design beam includes a 50km ITM lens, so I need to subtract that for more meaningful comparison; in the works.

For reference, the parameters used are:

• SRM to OM1: 3.4 m (Zemax gives 3.454 and I tweaked this slightly for fit), OM1 to OM2: 1.39 m (Zemax and in situ measurement)
• OM1 S: 1/4.6, OM2 S: 1/(1.7)