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  Sat Apr 24 15:05:41 2010, Kevin, Update, PSL, 2W Vertical Beam Profile vbp.jpg
    Reply  Sat Apr 24 15:50:47 2010, Koji, Update, PSL, re: 2W Vertical Beam Profile 
       Reply  Mon Apr 26 16:51:37 2010, Kevin, Update, PSL, re: 2W Vertical Beam Profile 
          Reply  Mon Apr 26 17:34:31 2010, Koji, Update, PSL, re: 2W Vertical Beam Profile 
             Reply  Tue Apr 27 15:29:16 2010, Kevin, Update, PSL, re: 2W Vertical Beam Profile vbp.jpgvbp_residuals.jpg
                Reply  Wed Apr 28 14:22:36 2010, Kevin, Update, PSL, re: 2W Vertical Beam Profile BeamFit.nb.tar
Message ID: 2838     Entry time: Sat Apr 24 15:50:47 2010     In reply to: 2837     Reply to this: 2846
Author: Koji 
Type: Update 
Category: PSL 
Subject: re: 2W Vertical Beam Profile 

1. The vertical axis should start from zero. The horizontal axis should be extended so that it includes the waist. See Zach's plot http://nodus.ligo.caltech.edu:8080/40m/2818

2. Even if you are measuring only the linear region, you can guess w0 and z0, in principle. w0 is determined by the divergence angle (pi w0/lambda) and z0 is determined by the linear profile and w0. Indeed your data have some fluctuation from the linear line. That could cause the fitting prescision to be worse.

3. Probably the biggest reason of the bad fitting would be that you are fitting with three parameters (w0, z0, zR) instead of two (w0, z0). Use the relation ship zR= pi w0^2/lambda.

ELOG V3.1.3-