4D Interferometer Alignment

Assembly

The drawing for the assembly is in the CAN 007s400b. There are two rail and fold mirror assemblies mounted to the telescope on the first vertical gallery pillar on each side. The rail bolts to a set of clamps mounted to the vertical pillar and uses a two pin interface. These allow the rail assembly to be repeatably removed for periodic recoating of the primary mirror. The top clamp pin is mated to a round hole and the lower clamp pin mates to one of the elongated holes in the rail. The clamps are positioned to locate fifth mounting hole from the bottom of the rail to be 196 mm above the bend in the vertical pillar.

Interferometer head installation and removal

The Phasecam 6000 interferometer head uses a dovetail interface base which allows removal from the lower rail carriage. This allows the interferometer to be moved from one side of the telescope to the other without realigning the fold mirror and rail carriages. A clamp screw on the dovetail base needs to be loosened to allow the head to be removed. When installing the head, make sure the clamp screw is tight.

Cable connections

Here are the cable connections for the Phasecam 6000: Three connections are made between the treehouse and the interferometer head mounted to the telescope: The 15-pin umbilical cable, a CameraLink cable, and the illumination fiber. The CameraLink cable uses a fiber repeater to extend the camera signal to distances greater than 10 m.

Fiber trigger

This box is mounted on the rear wall of the lower left treehouse. Connect a BNC cable between the external trigger input on the frame grabber and the trigger box. Connect the trigger fiber from the the adaptive secondary system to the FC fiber connector.

Network connection

In the lower left treehouse, connect the 4D computer to the top switch of sw0603.mountain (maybe marked as A, or 1) port 5 with Ethernet cable. IP address on the server is 192.168.18.180, gateway is 192.168.18.1. Subnet mask is 255.255.255.0 and the two DNS servers are 192.168.34.11 and 192.168.34.12.

4Sight operation

The interferometer PC can be accessed remotely using Windows Remote Desktop. Interferometer username 4D password 4D.

Fold Mirror alignment

Telescope at zenith. Retroreflector installed on the secondary mirror hub. A paper target is attached to the center of the back side of the secondary retroreflector. Set up the laser tracker on the primary mirror floor and locate the instrument in the telescope coordinate system. Identify the M3 vertex point using the laser tracker. This is point (DX) -7209.5 mm X -0.6 mm Y 2845.8 mm Z or (SX) 7210.5 mm X 1.87 mm Y 2842.2 mm Z in the telescope coordinate system. The laser tracker visible laser beam should be visible on the M3 vertex due to dust and coating imperfections. If it is not visible, a sheet of lens tissue placed over the M3 can be used. The lens tissue will need a small (-5mm) hole placed roughly over the M3 vertex. Remove the diverger to project the collimated beam from the interferometer head to the M3 surface. Use the TCSGUI to set the tip and tilt of the M3 to 0 and the selector angle to ?? deg. Align the fold mirror to overlay the collimated interferometer beam and the laser tracker beam on the M3 vertex to < 5mm. Observe the reflected collimated interferometer beam from the M3 on the ceiling of the telescope enclosure or on the M2 hub assembly. Rotate the M3 selector angle to position the reflected interferometer beam on the back of the secondary retroreflector. If the fold mirror carriage is not at the correct height on the rail, the reflected interferometer beam may miss the rear of the retroreflector completely. If this is the case, raise or lower the fold mirror carriage by a few mm and realign the fold mirror angle to overlay the interferometer beam and the laser tracker beam at the M3 vertex. Repeat until the collimated interferometer beam is overlaid with the laser tracker beam and centered on the target on the rear of the M2 retroreflector to within about 5 mm. Lock the carriage clamp for the fold mirror assembly. Remove any lens tissue on the M3.

Interferometer head alignment

Install the diverger. The focus of the interferometer is approximately 125 mm in front of the end of the diverger housing. The nominal distance between the interferometer focus and the fold mirror vertex is 924 mm. Adjust the position of the interferometer carriage to establish 1049 mm between the end of the diverger and the fold mirror vertex.

M2 alignment

Find the return image using a piece of paper with a hole at the output focus of the interferometer diverger. Tip/tilt the M2 using TCSGUI to center the return image on the hole in the paper. If a return image cannot be found near the focus, the short conjugate focus can be seen by looking into the M3 at the image of the front of the retroreflector glass pinhole formed by the M2. Adjust M2 tip/tilt until the beam is not vignetted by the glass pinhole. Remove the paper with hole from the interferometer output focus. When the return image is centered on the output focus, fringes should be visible using 4Sight over a portion of the pupil. Move the M2 in focus using TCSGUI to remove the focus fringes visible in 4Sight.

Tip/Tilt and focus the M2 using TCSGUI to minimize fringes using 4Sight. Focus the image of the pupil by using the hand paddle adjustment in the treehouse. The retroreflector spider vane obsuration can be used to fine tune the pupil focus. If the pupil image is not centered on the 4D camera left to right, the interferometer head can be pivoted using the 2 push screws on the interface plate between the dovetail mount and the interferometer carriage on the rail. If the pupil image is not centered top to bottom, the interface plate can be shimmed between the carriage and the interface plate. If the pupil image is adjusted, the tip/tilt of the M2 will need to be adjusted to restore zero tilt fringes.

Record the M3 selector angle and tip and tilt settings from TCSGUI. Convey these numbers to Software to update the Interferometer focal station default in TCSGUI.

-- %USERSIG{LeeDettmann - 2015-07-02}%

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