The mode profile of the green beam going through 40m cavity was measured.
According to the fitting the coupling efficiency to the cavity is 98.46% , but still the beam looks loosely focused .
This measurement has been done by using the oplev legs (entry #2957) to allow the beam to go through the 40m walkway.
With a beam scan set on a movable cabinet, I measured it along the 40m chamber.
Since the plot looks not so nice, I am going to work on this measurement a little bit more after I improve the mode matching.
Here is the parameters from the fitting
| target waist [mm] |
2.662 |
| measured waist x [mm] |
2.839 |
|
measured waist x [mm]
|
3.111 |
| |
|
| target waist position [m] |
43.498 |
| measured waist position x [m] |
42.579 |
| measured waist position y [m] |
38.351 |
I believe the error for the travel length was within 0.5 meter. The length was always measured by a tape measure.
A thing I found was that: spatial jittering of the beam gets bigger as the beam goes further. This is the main source of the error bar for the spot size.
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