with Lucia and Kokeyama-san

We arranged the telescope according to 11486. Today, we meaured the beam profile after the BS (RBS3) behind the second lens (RLNS2). At the beginning, we saw very strange horizontal beam shape so we put a half-wave plate between HBS1 and RST1 and switched RBS3 to a polarization BS so we can get better S Pol with the camera. Figure 1 shows the S Pol reflection after the PBS but the beam shape is still strange. For reference, Figure 2 is the P Pol beam whereas figure 3 is the beam with the original setup without half-wave plate and polarization BS.

We proceed to charaterize the beam anyway, eventhough the beam shape only gets stranger as it propagates.

From the design in I did in 11486, the beam waist should be at around 1 m away from RLNS2 or RBS2. However, as can be seen from the fit in figure 4, horizontal beam waist is at negative displacement whereas vertical beam waist is at around 3 m away (fitting probably not precise as we didn't get enough measurements). The beam also flattens as it propagates and the beam profile is nowhere near gaussian.

Plus, we found that the optics are all covered with dusts. See figure 5, the first lens (RLNS1) as an example.