R&D (FilterCavity)
YuefanGuo - 11:30, Wednesday 25 September 2019 (1659)
AA telescope new design works for less astigmatism beam both axises

According to the measurement yesterday, we made the new design for the telescope, this time seems we could use one telescope to get gouy phase around 90 degree difference in two axis of the beam.

 

Firstly, we calculated the reflection beam waist position according to the measuremnt. (colors refer to different curves in last entry)

 

Measured beam waist

Measured beam waist position (origin @ FI)

Calculated waist of the cavity reflection beam

Calculated waist position of the cavity reflection beam

(origin@FI)

Axis 1 (blue)

41.8um

1.8351m

571.271um

-5.756m

Axis 2 (orange)

73.56um

1.86m

541.055um

-2.446m

 

The size of the waist in two direction seems much closer than all the measurement we did before.

Then because the space limitation, we fixed the two quadrant position as before, which is around 1.9m and 2.3m from the FI, and both the positions have some margin of 5cm.

The beam we used to first determine the lens is the orange one, because it has smaller divergence than the other one. So with the orange as the initial beam, we tried to put different focal length, and move the lens position to have the beam waist around 2.1m which is in the middle of the two quadrants. By checking the gouy phase difference, we could know that we need longer focal length or shorter.

The final results we got is to put a lens with focal length of 1m, and 0.82m from the FI. 

Then the quadrants information are as below

 

Distance between the lens and quadrant

Gouy phase on the quadrant

Beam size on the quadrant

QPD1

1.08m

99.6

0.26mm

QPD2

1.5m

188.7

0.27mm

 

Then use the distance to calculate the gouy phase of the other beam axis (blue). By slightly adjusting the lens position and the quadrants position, we could get the gouy phase difference around 90 degree for both axises. In this case the lens position is 0.75m.

 

Distance between the lens and quadrant

Gouy phase on the quadrant

Beam size on the quadrant

Gouy phase difference

QPD1 (axis 1)

1.15m

111.1

0.23mm

84.2

QPD2 (axis 1)

1.58m

195.3

0.33mm

QPD1 (axis 2)

1.15m

148.9

0.1mm

94.1

QPD2 (aixs 2)

1.58m

243.0

0.73mm

Comments related to this report
YuefanGuo - 10:54, Thursday 26 September 2019 (1660)

This is the scheme of the AA telescope now