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Final Focus Lens Damage

On checking the laser alignment over the weekend the FF lens was discovered to be severely damaged. It has damage spots inside the body of the lens that look like the shape of the focused laser beam and are repeated in a line where the chamber and lens have moved. There is also a bright spot observable on the f = 100mm post IP lens and it is thought that there is some damage to this optic and it is refocusing a small reflected beam back into the FF lens.

The FF lens has been put back onto the chamber (hopefully to be replaced by the undamaged one which is being shipped from the UK). The f = 100mm lens has been replaced by a PC f = 150mm lens (not showing the bright reflected spot) and the lens holder has been moved several cm away from the chamber window. The post IP turning mirror has been taken off the stage, mounted on a tall pedestal and placed on the optical table and the energy meter + attenuator have also been moved to dump the beam from the mirror. This line has not been properly aligned with the laser beam and this should be checked before running. The lens replacement may also have affected the alignment into the APD so it should also be checked - is there still a reasonable laser signal on the APD or does it need moving?

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Topic revision: r1 - 11 Dec 2011 - LauraCorner

 
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