Madi, Camilla, TJ

Last week we changed the lenses in the HWS path, to get an unclipped beam from the OzOptic 532nm laser (installed 89993) through the transmon and back out. The lens chain was designed so that the beam matched the ALS beam at M11 ie the PBS (ALS beam measurements 90370). The goal is to verify lens design methods, as well as get another measurement of the 'badness' affecting the beam in-vacuum. 

New lenses and positions:

L3: f = -559mm, position: 7cm from M4, between M4 and Pol

L2: f = 1000mm, position: 15cm from M3, between M3 and BS2

L1: f = 2200mm, position: 26cm from M3, between M3 and BS2

The into-vacuum beam was measured after M11 and picked off the path using the Pellicle beamsplitter, before being put through a lens to make the beam small enough to be measured by the Nanoscan. Nanoscan images attached. The ingoing beam is nice and round, no astigmatism. 

The return-from-vacuum beam was measured in the same location, and again picked off using the Pellicle and focused through a lens in order to measure. Images attached. Once again, the two-lobed pattern was observed, consistent with the measurements taken of the ALS a few weeks ago ( 90370). This time without the ellipticity, which was due to the in-going ALS beam shape. 

Next steps are to verify the design of the lens chain with the real life measurements, and determine if the shape of the return-from-vacuum beam is too 'bad' to be used in a HWS measurement.