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Entry  Mon Mar 26 23:47:54 2012, Suresh, Update, IOO, Beam Profile measurement: IPPOS beam BeamProfile_IPPOS.pngBeamProfile_IPPOS.pdfBeamProfileData_IPPOS.xlsx
    Reply  Tue Mar 27 02:05:40 2012, Suresh, Update, IOO, Beam Profile measurement: IPPOS beam BeamProfile_IPPOS.pngBeamProfile_IPPOS.png
       Reply  Tue Mar 27 11:54:18 2012, Jenne, Update, IOO, Beam Profile measurement: IPPOS beam IPPOS_distances.pdf
          Reply  Tue Mar 27 18:03:46 2012, Jenne, Update, IOO, Beam Profile measurement: IPPOS beam BeamProp_usingMeas2012MMTnumbersLowRes.png
             Reply  Tue Mar 27 21:20:32 2012, Jenne, Update, IOO, Beam Profile measurement: IPPOS beam BeamProp_usingMeas2012MMTnumbersLowRes.png
                Reply  Tue Mar 27 23:37:35 2012, Suresh, Update, IOO, Beam Profile measurement: IPPOS beam Beam-Profile_IPPOS_wError.png
                Reply  Wed Mar 28 01:17:29 2012, Jenne, Update, IOO, Beam Profile measurement: IPPOS beam BetterDistances_IPPOSLowRes.pngBetterDistances_MainIFO_PRMnormalLowRes.pngBetterDistances_MainIFO_PRMflippedLowRes.png
                   Reply  Wed Mar 28 18:26:47 2012, Jenne, Update, IOO, Beam Profile measurement: IPPOS beam OptimizedMMT_halfMeterChange_IPPOSviewLowRes.pngOptimizedMMT_halfMeterChange_IFOviewLowRes.pngOptimizedMMT_pt2cMeterChange_IPPOSviewLowRes.pngOptimizedMMT_pt2cMeterChange_IFOviewLowRes.png
                      Reply  Wed Mar 28 20:54:02 2012, Jenne, Update, IOO, Beam Profile measurement: IPPOS beam MMT_moved_by_1pt3meters_MMT1th_25_MMT2th_12_LowRes.pngMMT_moved_by_1pt3meters_MMT1th_25_MMT2th_12_LowRes.png
                         Reply  Mon Apr 2 18:58:32 2012, Jenne, Update, IOO, Beam Profile measurement: IPPOS beam NonOptimized_propagatedWaistPlotted_LowRes.png
                         Reply  Mon Apr 2 23:06:38 2012, Suresh, Update, IOO, Beam Profile measurement: IPPOS beam: Mystery deepens 40mOpticsLocations.pdfBeam-Profile_IPPOS_wError.pdfBeam-Profile_PRM_1_wError.pdf
       Reply  Tue Mar 27 17:19:02 2012, Koji, Update, IOO, Beam Profile measurement: IPPOS beam 
    Reply  Tue Mar 27 02:18:31 2012, keiko, Update, IOO, Beam Profile measurement: IPPOS beam text9149.pngfirst_cap.pngsecond_cap.pngtext9149.png
       Reply  Tue Mar 27 16:06:59 2012, keiko, Update, IOO, Beam Profile measurement: IPPOS beam 
Message ID: 6477     Entry time: Mon Apr 2 23:06:38 2012     In reply to: 6462
Author: Suresh 
Type: Update 
Category: IOO 
Subject: Beam Profile measurement: IPPOS beam: Mystery deepens 

Quote:

I fitzed by hand with the numbers for the incident angles on MMT1 and MMT2, and then let the code optimize the position of MMT1 and MMT2.

Here I have set the incident angle for MMT1 = 25deg, and MMT2 = 12deg (should be 3.5deg, 1deg by design).  The length of the telescope doesn't want to change by more than 7mm, but the position of the telescope wants to change by 1.3meters.     Is it possible that the distances on the Monday IPPOS measurements aren't actually correct?

 

I am trying to track down possible errors in our measurements. 

So as a first step I am recomputing the IPPOS waist location with respect to the MC waist, using the same optical layout diagram as the one used by Jenne in her calculations.  Pic of Jenne's lab notebook showing location of optics is attached.  

IPPOS: measurement elog 6459: Vertical Std.Error Horizontal Std.Error
Waist  2.768 mm 5 microns 2.476 mm 10 microns
Waist location from MC waist  12.411 m  17 mm  9.572 m 54 mm

Std Dev of residuals from fit function

  37 microns   54 microns

 Let us compare it with the old measurement of the IPPOS beam from June/18/2010.

IPPOS: measurement June 18th 2010 Vertical Std.Error Horizontal Std.Error
Waist  2. 812mm 8 microns 2.909 mm 20 microns
Waist location from MC waist  9.265 m  224 mm  5.869 m 415 mm

Std Dev of residuals from fit function

  ~ 25 microns   ~25 microns

Note that there is a discrepancy of about 3.2 m in the waist location for the vertical profile and about 3.5 m for the horizontal profile between these two measurements. 

Let us compare these measurements with what is expected from calculations.  Jenne uses the known parameters of MC waist and the locations of the MMT optics to compute the parameters for the IPPOS beam:

IPPOS: Jenne's Calculations elog 6476:

Vertical Std.Error Horizontal Std.Error
Waist  2.844 mm   2.894 mm  
Waist location from MC waist  11.019 m   8.072 m  

 As the 2010 measurements are reported wrt to MMT2 and calculations are wrt MCwaist, I have used the distance between the MCwaist to MMT2 = 3.910 m to shift the reference from MMT2 to MC waist. Refer to the attached diagram from Jenne's notes for this MMT2 <--> MC waist distance.

There is a discrepancy of 1.5 meters between the calculations and recently measured waist location.  The discrepancy with the 18Jun2010 measurement is much larger, about 3 meters in both v and h.

Are such variations to be expected between two successive measurements?  I looked at another case where we have two measurements of a beam to see what to expect.

I looked at the REFL (Reflection from PRM) case, where we repeated a measurement, to see how much variation could happen in w0 and zr, between repeated measurements. This was a particularly bad case as our first attempt had problems due to OL servo loop oscillations in the PRM suspension damping.  We fixed that later and measurement 2 has smaller residuals. And I think we are doing okay in IPPOS case as seen by the reduced scatter of the residuals.

 These are the fits from the REFL beam measurement 1

REFL: Reflection from PRM: measurement 1 Vertical Error Horizontal Error
Waist 1.662 mm 4 microns 2.185 mm 4 microns
Waist location from MMT2 after reflection at PRM 1.781 m 17 mm 4.620 m 53 mm
Std.Dev. of residuals from fit function   61 microns   98 microns

 I have also recomputed the fits to the data from REFL beam measurement 2.  They match the earlier fits reported by kiwamu in his elog 6446

REFL: Reflection from PRM: measurement 2 Vertical Error Horizontal Error
Waist 1.511 mm 3 microns 2.128 mm 3 microns
Waist location from MMT2 after reflection at PRM 1.281 m 9 mm 3.211 m 37 mm
Std. Dev of residuals from fit function   58 microns   61 microns

 

Note that between these two measurements the beam waist location has shifted by 0.5 m for the vertical and about 1.3 m for the horizontal cases.  So variations of 1.5 m in the waist locations are possible if we are not careful.  But this is a particularly extreme example, I think we are doing better now and the measurement is unlikely to change significantly if we repeat it.

Some notes:

Fits for IPPOS and both REFL measurements 1 and 2 are attached. 

The zero reference for the z axis of the IPPOS beam plot is at a distance of 6.719 m from MC waist for a beam propagating towards the IPPOS QPD.

The zero reference for the z axis of the REFL beam plots is at a distance of 5.741 m from the MMT2 in the direction of a beam reflected by PRM and propagating towards the REFL port.

 

Attachment 1: 40mOpticsLocations.pdf  1.214 MB  Uploaded Mon Apr 2 20:56:28 2012  | Hide | Hide all
40mOpticsLocations.pdf
Attachment 2: Beam-Profile_IPPOS_wError.pdf  74 kB  | Hide | Hide all
Beam-Profile_IPPOS_wError.pdf
Attachment 3: Beam-Profile_PRM_1_wError.pdf  71 kB  | Hide | Hide all
Beam-Profile_PRM_1_wError.pdf
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