Georgia, Laurence and Dripta

We went to the Y-end to take a beam profile of the ALS green beam. We placed a beam profiler at various positions in the path of the green laser and took note of the beam position, shape and size.


Beam position for the beam going just before the periscope:

Reference mirror              Distance from the Reference Mirror(cm)              Beam position X (micrometer)              Beam position Y(micrometer)

ALS M7                                                    14.6                                                                  5070                                                  4320
ALS M7                                                    16.5                                                                  4675                                                  4165
ALS M7                                                    20.0                                                                  4707                                                  4135
ALS M7                                                    24.8                                                                  4840                                                 4120
ALS M10                                                  10.6                                                                   5210                                                 4373

Beam position for the beam on the reflection side:

Reference mirror              Distance from the Reference Mirror(cm)              Beam position X (micrometer)              Beam position Y(micrometer)

ALS M17                                                   7.6                                                                      1180                                                   980


The above table shows that the beam propagation is pretty consistent.

For the beam shape, please look at the attached screenshots. The first one(beam_entering.png) is that for the beam just before the periscope and the second one is for the reflected beam (beam-refl.png). It is worth noting that they are both elliptical (egg-shaped). 

The last thing we did was take a bunch of pictures of the green beam from the viewport where the ETM camera is. One of those pictures(the most clear one) is attached. It looks like that beam is not exactly centred.  

The table layout can be found in here : https://dcc.ligo.org/DocDB/0114/D1400241/007/D1400241_ISCTEY_H1_V7%20copy.pdf