Miyakawa, Tanaka

## Abstract

• We measured the beam profile aling with IR QPD path after first lens (RLNS1) (https://gwdoc.icrr.u-tokyo.ac.jp/DocDB/0089/T1808962/009/20211214_TMSY_AsInstalled.png). 
  • beam waist diameter x: 38.1 um
  • beam waist diameter y: 38.3 um
• These values is consistent with the value in klog1205
• Then we 

## What we did

• First, I checked the current optics around the TMS QPD. Currently, almost everything is in place as shown in klog12721's photo, only the T=2% BS has been removed.
• Next, I placed a mirror between the BS between the GR filter and the lens 2 and the TMSX IR QPD2 to pick up the light for the beam profile. Figure 1 shows the beam profile measurement system.
• I measured the beam profile along the axis of the picked-up light. Figure 2 shows the result. The zero point in this figure is where GR is 10 holes away from the GR filter, or 250 mm. Fig 3 shows the beam at around 150 mm. And then I obtained the size of the beam waist by fitting their measurement data. 
• The following are the x- and y-axis beam sizes for the laboratory system.
  • x (lab): 38.1 um
  • y (lab): 38.3 um
• This result is consistent with the previous measurement (klog12052).