| 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.
|