Earlier I posted a beam profile of the north laser path that seemed to have much greater uncertainty on the horizontal axis (see: https://nodus.ligo.caltech.edu:8081/CTN/1646). Antonio was a little concerned that maybe the iris or something else was clipping, this might have caused some defraction.
I cleaned the first window and replaced the second window with another W2-PW1-1037-UV-45P (AR coated on both sides), then the profiling camera was realigned. A couple of screen shots are attached of the beam profile at a couple of points, it doesn't look nicely Gaussian close in, I'm not sure what is causing this, but this is the beam directly from the laser (via two windows).
The profiles were fitted using the D4σ method (standard and default) to find the 1/e^2 drop off of the beam radius (as was done in all the previous posts).
This time the data looks better for the horizontal.
The data is as follows:
z= [0 25 100 125 150 175 200 225 250 300 325 350 375 400 425]*1e-3 + (72e-3+24e-3+63e-3); % Distance from the laser head. The fixed added on value at the end is the distance to the first measurment point
W_horz = [752.9 804.0 957.5 1010.9 1077.6 1136.6 1190.7 1244.2 1301.1 1407.0 1461.6 1513.9 1585.5 1622.6 1668.0]*1e-6/2; % Horizonal beam radius
W_vert = [696.0 754.0 995.0 1066.2 1130.2 1210.7 1286.8 1356.9 1414.7 1580.1 1642.9 1697.5 1786.8 1859.7 1951.1]*1e-6/2; % Vertical beam radius
And fitted values are:
Horz. beam waist = 272.0952 um
Horz. beam waist position = -60.2164 mm
Vert. beam waist = 216.5147 um
Vert. beam waist position = -22.9082 mm
These are very similar to the previous measurement. Plots and configuration schematic are attached.