Kitazawa, Aso

We checked the beam spot positions on the PR3 and BS.

The method is simple. I put a sensor card with a ruler attached in front of the mirrors. Then Kitazawa-kun took photos.

Actually, it was difficult to get pictures of the beam spot on the sensor card. We need to make the ambient light low to see the spot but then the photo becomes too dark (the small bright spots are OpLev beams). So I decided to do the following.

Firstly, we turned off the light and I adjusted the position of the card so that the center of the card coincides with the center of the beam spot. The definition of the center of the card is the center of the + mark formed by the boundaries of the 4 cards. While keeping the position of the card unchanged (as much as I can), we turned on the light and took pictures. So in the following pictures, even if you cannot see the beam spot, the center of the + shape is the center of the beam spot.

Of cource, this method is not so precise. First of all, it is not so easy to identify the center of the beam because it is somehow distorted. Secondly, I'm was not able to maintain the position of the card completely unchanged. I think the error bar is up to 1cm.

The pictures we took (selected only nicely focused ones) are uploaded below:

PR3: https://www.dropbox.com/sh/56aavh5ci2bgtzd/AACwtSY7QrrFsAmvpg_fW6Csa?dl=0

BS: https://www.dropbox.com/sh/rnucdjvy0nzvtpe/AADtC_ulYpm6dJA4rXCMqndEa?dl=0

X and Y mean pictures to measure the horizontal and vertical positions. For example, when taking a picture for X of PR3, Kitazawa-kun took the picture from below but horizaontally aligned with the center of the mirror to avoid parallax.

From the picture, the beam spot position on each mirror can be roughly estimated as follows:

PR3:  3mm left, 15mm down from the center.

BS: 30mm -10mm = 20mm right, 8mm down from the center.

(For BS, the sensor card is put 1cm away from the HR surface and the beam is incident at 45deg. angle. Therefore, the horizontal position is offset by 1cm on the sensor card.)