40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log  Not logged in ELOG logo
Entry  Mon Aug 17 02:05:49 2009, Yoichi,rana, Update, PSL, Reference cavity reflection looks bad P8170113.JPGUntitled.png
    Reply  Mon Aug 17 04:16:13 2009, Yoichi, Update, PSL, Reference cavity reflection looks bad 
Message ID: 1915     Entry time: Mon Aug 17 02:05:49 2009     Reply to this: 1917
Author: Yoichi,rana 
Type: Update 
Category: PSL 
Subject: Reference cavity reflection looks bad 
Rana, Yoichi

It has been a well known fact that the reference cavity reflection beam looks ugly.

We measured the visibility of the RC by locking and unlocking it.
Comparing the reflected beam powers, we got the visibility of 0.46,
which is pretty bad.

The beam going into the RC looks fine (circular on a sensor card).
However, the beam reflected back from the RC is distorted into a
horizontal ellipse, even when the RC is not locked.

We took a picture of the reflected beam hitting a white paper with the
infrared camera (see the attachment). It looks like two overlapping
circles horizontally separated. Could it be a badly coated optics
producing a secondary reflection ?

We looked into the RC's front mirror with an inspection mirror, but we
could not identify any obstructing object.

Rana is now touching the RC alignment.

We plan to remove the periscope before the RC to have a better look
into the cavity for inspection.

Late breaking update:
- We also moved the Refcav reflection camera to look at the leakage through a reflection steering mirror so that there's less chance of distortion. There was previously a W1 window in there as a pickofff. Also changed the camera to autogain so that we can see something.

- Re-aligned onto the refl pd.

- Tweaked alignment into RC. Mainly in yaw. Transmission went from 5V to 7V. In your face, Aso!
Attachment 1: P8170113.JPG  66 kB  | Hide | Hide all
Attachment 2: Untitled.png  130 kB  Uploaded Mon Aug 17 03:27:30 2009  | Hide | Hide all
ELOG V3.1.3-