40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  OMC elog  Not logged in ELOG logo
Entry  Thu Apr 18 20:47:54 2019, Joe, Optics, , OMC initial alignment and locking IMG_7676.JPGIMG_7666.JPGIMG_7670.JPGIMG_7883.JPGIMG_7882.JPG
    Reply  Fri Apr 19 11:34:19 2019, Koji, Optics, , OMC initial alignment and locking misalignment1.pdf
Message ID: 346     Entry time: Thu Apr 18 20:47:54 2019     Reply to this: 349
Author: Joe 
Type: Optics 
Subject: OMC initial alignment and locking 

[Joe, Phillip, Koji, Stephen]

*draft post, please add anymore info if I missed something*

  • made initial alignment of the cavity. To do this we used the periscope mirrors to aim the incoming beam at the centre of the first mirror and second (1st curved mirror) mirror. Using the micrometers (initial positions was 0.20mm), we moved the first curved mirror so that it hit the third mirror. We then used a combination of the periscope and first curved mirror movements to start seeing 2 or 3 round trips. micrometer was set to roughly 0.11mm. We then only used  periscope mirrors to align the beam into the cavity.
  • We set up a wincam at the transmission of the cavity. This was a useful was of seeing what mode was being transmitted through the cavity. We walked the beam with the periscope mirrors until we saw flashes of the TM00 mode.
  • Once the cavity was transmitting TM00 modes, we started to lock it. Once it was locked we looked at the the spot positions of beam on the mirrors. Phillip looked with an IR viewer and could see that the spots were too high on both the curved mirrors
  • We set up a CCD to capture an image of this. Two post holders have been left in place for easy movement of the CCD.

General notes about working with this set up. The lens on the CCD can come off quite easily, as you just change how much its screwed on to change the focus. Care should be taken that you don't know the template with this as well, as the camera is quite close to the template (and near the edge of the bench!). Also be mindful of the PZT wires, as they can pull the mirrors out of position.

Attachment 1 shows the position of the spots on the mirrors A14 and PZT11. The spots are about 3mm ish from the centre of the curved mirror in the vertical and horizontal direction. 

Attachment 2 sketch of mirror positions.

Attachment 3 shows the postion of the spot on PZT13. The spot is less near the edge than on PZT11, but its still 2mm ish from the centre of the curved mirror in both directions.

To move the beam horizontally we can use the alignment matrix in appendix C of T1500060. However since we don't have control over the pitch of the mirrors, moving the spots down could require us to inspect the glass breadboard/prisms for dust. We suspect that PZT could be the culprit, as we could not see newtonian rings between its base and the glass breadboard. One way to test this idea is just to clean the bottom of the PZT with acetone, and see if that improves the spot position. If we don't have to do any work to realign it, then this was not the issue.

Koji pointed out that the spot in attachment 1 is very near the edge of the optic, so shifting the beam horizontally could also fix the vertical issue. 

Attachment 1: IMG_7676.JPG  3.819 MB  Uploaded Fri Apr 19 08:20:58 2019  | Hide | Hide all
Attachment 2: IMG_7666.JPG  2.934 MB  Uploaded Fri Apr 19 08:22:21 2019  | Hide | Hide all
Attachment 3: IMG_7670.JPG  3.149 MB  Uploaded Fri Apr 19 08:27:27 2019  | Hide | Hide all
Attachment 4: IMG_7883.JPG  1.654 MB  Uploaded Fri Apr 19 10:18:17 2019  | Hide | Hide all
Attachment 5: IMG_7882.JPG  1.681 MB  Uploaded Fri Apr 19 10:19:03 2019  | Hide | Hide all
ELOG V3.1.3-