KAGRA Logbook

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IOO (Laser Bench)

yutaro.enomoto - 22:16 Thursday 13 April 2017 (2679)

bKAGRA PSL

[Kokeyama, Enomoto]
(4/13, 14)

We put some optics including a Faraday isolator on the light path from the 2W laser. Transmissivity of the FI was (726mW / 808mW =) 90%, which seems OK.

Then, we did mode matching work. To make the beam shape coincide with that of the final bKAGRA high power laser beam, we put lenses as designed (Lb and Lc; see PSL layout) but the resultant beam profile was not as desired.
According to the result we had got, we replaced and relocated lenses to try to make the beam closer to the design. The current beam profile is shown in the attached figure. We need to relocate the lenses a little bit more (~ a few cm) tomorrow.

Current top view of the light path can be seen in the attached picture.

Images attached to this report

Comments to this report:

yutaro.enomoto - 16:27 Friday 14 April 2017 (2684)

[Kokeyama, Enomoto]

According to the beam profile result we had got yesterday, we relocated the two lenses and the result is shown in the attached figure.
The current beam profile seems to match the designed one to some extent.
Hyperbolic fitting does not work very well because the shape of the beam gets dirty as the beam goes far from the waist, so the profile we have now is probably the best one that we can achieve. Thus we decided to fix the beam profile as is.

= Next =
put two lenses to make the beam profile coincide with PMC's as soon as high power compatible lenses arrive.

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