Camilla, Sophie

We reprofiled the QCL unit 0970 because we were concerned the SNR was too low and effecting the profile of the beam (see alog 92242). The 99:1 BS placed in front of the QCL was replaced by the CO2 99:1 BS which at 4.6um acted effectively as a 70:30, with the 30% beam transmitted. We profiled the 30% beam at 1A and 25C over a 50cm range. 
The strange beamsize fluctuations around the waist were observed again so we concluded this was a not a measurement error and slightly non-gaussian behaviour of the beam.
The complex q parameter for the laser was found using a non linear fit to be:

--- Horizontal (A1) Fit ---

Data range: z = [97.0, 597.0] mm
Beam radii: [422.0, 1412.3] µm
Fit converged: w₀=411.4+/-9.2 µm, z₀=224.9+/-3.9 mm
q = -225+/-4 + 116+/-5i mm

--- Vertical (A2) Fit ---

Data range: z = [97.0, 597.0] mm
Beam radii: [413.6, 1183.7] µm
Fit converged: w₀=421.0+/-10.9 µm, z₀=293.7+/-3.9 mm
q = -294+/-4 + 121+/-6i mm
Note: Louis pointed out the plots of the fit have weird error bars which I will investigate in the QCL fitting code. 

The measured q-parameter is very similar to the Y-arm unit and a very similar telescope optimisation could be completed. This layout is listed in the git and has the following beamsize and astigmatisms. 

Beamsize at ITM
wx_ITM: 53.299 mm
wy_ITM: 52.042 mm
w_ITM_mean: 52.671 mm
w_ITM_astig: 1.257 mm

This is an improvement in astigmatism of approximately 7mm from the 0922 unit we swapped out.

We are currently aligning the table and the beam is aligned up to the PDBS. Unfortunately, many of the other optics had to move to ensure the PD intensity noise measurement optics would not be positioned in the waist so they do not get burnt.