The compressor NF/FF cameras setup should be relatively stable and rarely, if ever, require realignment of the internal optics. If alignment is necessary, the setup uses silver mirrors so that it can be re-aligned with a visible diode laser. The full alignment procedure is presented first.

A more likely drift is between the compressor NF/FF setup and the compressor gratings, especially because the compressor gratings move with each vent/pump-down cycle. In this case, the steering into the setup needs to be changed without internally adjusting the setup or changing the alignment through the compressor.

Compressor NF/FF Internal Alignment

Use this procedure to realign the imaging systems internal to the compressor NF/FF setup and then align the IR laser into the setup. 

The IR laser alignment must be correct through the compressor in order to successfully align the IR laser into the setup. This means the laser must be exiting the compressor chamber close to centered and perpendicular on the exit window. If not, the beam is not, the mirrors inside the compressor will need to be adjusted moved before beginning.

Required Tools/Hardware

Gather these ahead of time and bring them down to the tunnel to save time.

1. Visible diode laser mounted in a kinematic mount.
2. 1in post assembly to mount the diode laser above the periscope. About 14in tall with the diode cantilevered 4in off the side.
3. Wavefront camera mount block (Part No. 008-022) with a Mako camera mounted to it.
4. POE injector and cables for the Mako camera.

Diode Laser Alignment

Install a visible diode laser and adjust the mirrors and lenses to align the setup.

1. Remove the periscope enclosure and the top and front panels of the enclosure.
2. Build a 1in post assembly to mount a visible diode laser on a kinematic mount pointing down above the upper periscope mirror (M1).
3. Remove the ND filter+lens stack from the translation mount between the two periscope mirrors (ND3 and L1).
4. Center the translation mount in its range of motion.
5. Adjust the position and angle of the diode laser to align the beam to the translation mount and the iris immediately after the lower periscope mirror (M2).
   1. To center the laser on the translation mount, use a 2in round piece of orange paper with the center marked (see Figure 1).
   2. Alternatively, use an SM2 threaded iris mounted to the translation mount.
6. Use the lasers kinematic mount and the lower periscope mirror (M2) to align the beam to the two irises after M2 (IR1 and IR2, see Figure 2).
7. Remove the near field filter and lens (ND4 and L2).
8. Look at the output of the NF camera, use M3 to align the beam to the center of the camera chip.
   1. Check the back reflection from BS1 on IR2. 
   2. If it is very far off vertically, use the adjustment screw on the BS1 mount to adjust.
   3. If it is very far off horizontally (avoid doing this unless it is really far off), adjust M3 to center the back reflection. Loosen the clamping fork and rotate the mount to center the beam on the NF camera. Iterate until converged.
   4. If the beam is no longer centered on the BS1, translate BS1 and repeat.
9. Record the position of the beam center on the chip.
10. Reinstall L1 and adjust the lens translation to center the laser spot on the reference position from the previous step.
11. Move the NF translation stage to the furthest position from L2, record the position of the laser.
12. Install L2 and adjust its translation to center the spot on the NF, adjust the tilt to align the back reflection to IR1.
13. Look at the output of the FF camera, use M4 to center the beam on the camera.
    1. The camera exposure will have to be turned way up and it may be helpful to remove ND5. 
    2. Lens L3 is pre-set with an autocollimator to have its focal plane on the camera chip, don't touch it.
    3. The microscope objective's longitudinal position will be optimized later using the IR beam.
14. Install the wavefront camera mount block on the wavefront sensor stage.
15. Remove the wavefront sensor lens and ND filters (L4, ND7 and ND8).
16. Flip in M5 and adjust M5 so that the beam is centered on the camera. Record the beam position.
17. Install L4 and adjust the lens translation until the beam is centered on the reference position from the previous step.
18. Install the ND filters (ND7 and ND8).

IR Alignment

Overlap the IR with the visible laser and set the imaging planes for the different systems. 

No one has done this with the main laser, it might be impossible to see with the IR viewer.

If one doesn't want to check the alignment through the compressor, this can be done with the compressor under vacuum.

1. Ensure all ND filters are installed if using the pulsed laser (particularly ND3, the MO is at risk of burning otherwise).
   1. The ND flipper should be out.
   2. If using the fiber laser, ND3 can be left out, all other ND filters still need to be installed.
2. Turn off the visible diode laser, turn on either the main laser or the fiber laser.
3. Ensure the alignment through the compressor gratings is good before starting.
   1. Set the iris size upstairs to -5mm.
   2. Check the beam alignment by placing the compressor iris (normally left sitting in the bottom of the chamber) in the two post holders before the first grating.
   3. Verify with an IR viewer that the incoming and outgoing laser spots on the first grating are vertically aligned.
   4. Make sure to remove the iris when done.
4. Use CP-M7 (see Figure 3) in the compressor and the top periscope mirror (CC-M1) to align the laser to IR1 (with CP-M7) and IR2 (with CC-M1).
   1. This works very well with the fiber laser and an IR viewer. Lean some orange paper up against CC-M3 and look at it with the IR viewer. A nice, clear spot should be visible.
5. If all goes well, the beam should be visible on both the NF and the FF cameras.
   1. The position on the cameras can be used to tweak the steering into the setup.
   2. ND3 will need to be reinstalled to prevent saturation on the camera.
   3. Always double check that the laser is going through the irises - they serve as the master references.
6. Adjust the longitudinal position of the microscope objective to minimize the spot size on the FF camera.
7. Insert an imaging target in front of the DM.
8. Adjust the longitudinal position of the NF camera to image the target.
9. Adjust the longitudinal position of the WF camera to image the target.
10. Shutter the IR laser.
11. If using the fiber laser, install ND3.
12. Remove the diode laser and replace all enclosure panels.

Resetting the Alignment References

Periodically, the alignment through the compressor gratings will need to be reoptimized. When this happens, the alignment onto the compressor NF/FF cameras will change. The beam may potentially walk off the FF camera and the previous reference positions will no longer represent the optimal alignment through the compressor. In this case, the alignment into the compressor NF/FF setup will need to be adjusted and the reference positions reset.

Adjust mirrors between the compressor gratings and the imaging setups to get the laser spot centered on the cameras again.

1. Ensure all ND filters are installed if using the pulsed laser (particularly ND3, the MO is at risk of burning otherwise).
   1. The ND flipper should be out.
   2. If using the fiber laser, ND3 can be left out, all other ND filters still need to be installed.
2. If the laser is not visible on either the NF or FF cameras:
   1. Use CP-M7 (see Figure 3) in the compressor and the top periscope mirror (CC-M1) to align the laser to IR1 (with CP-M7) and IR2 (with CC-M1).
      1. This works very well with the fiber laser and an IR viewer. Lean some orange paper up against CC-M3 and look at it with the IR viewer. A nice, clear spot should be visible.
   2. If all goes well, the beam should be visible on both the NF and the FF cameras.
3. Fine-tune the steering onto the cameras. 
   1. Use the top periscope mirror (CC-M1) to align the laser to the near field camera.
   2. Use CP-M7 (see Figure 3) in the compressor to align the laser to the far field.
   3. It can be convenient to align the laser back to the previous reference positions. Then confluence/auto-aligner/etc. don't have to be updated.
4. Double check that the laser is going through the irises - they serve as the master references.
   1. If it is not, then internal alignment is required. Perform the above Compressor NF/FF Internal Alignment.
5. Record the positions of the laser on both cameras.
   1. Save the image and stats to the E-log for both cameras.
   2. Update the positions in confluence: Camera Alignment References