LGS Alignment Procedures

AO LGS Optical Alignment

1. Install 600nm dichroic instead of mirror in 2nd dichroic mount.
2. Put in alignment laser (need to remove first turning mirror).
3. Start APD TT software (LickAO - AO Loops - LGS APD Tip/Tilt).
4. Turn off TT Drive from the Power Control window. Note: don't do this step with new LGS7 APD code--leave in NGS mode.
5. Put TT mirror in E-Null position
6. Align through all pinholes with alignment laser
7. Coarse align to IRCAL (hit target on IRCAL dark cover). Note that this should not be necessary if the NGS alignment was good.
8. Measure where alignment laser lands in IRCAL field. The alignment laser is a large spot on IRCAL, so record center of spot as best you can.
9. Put in red light point source.
10. Move FiberStage X and Y so that the red light point source is centered on the same spot as the alignment laser. Aligning within a few pixels is sufficient.
11. Align into slow WFS.
    1. Take exposure with slow WFS.
    2. Move TT cube to adjust centering (or the small turning mirror in front of the slow WFS).

       TTCube Y-axis: -counts moves spots right, +counts moves spots left
       TTCube X-axis: +counts moves spots up, - counts moves spots down typical moves are a few thousand to a few hundred

    Note: don't do this step with new LGS7 APD code--leave in NGS moden
12. Align APD TT sensor.
    1. Turn off red light source.
    2. Install the Oriel white light source and turn brightness all the way up.
    3. Connect fiber from white light source to APD fiber #1 (back propagation).
    4. Put paper target on DM.
    5. Examine centering of back propagation on DM target.
    6. Do steps c-e with the other 3 fibers.
    7. Determine if majority of fibers have the same centering, if so, move the small beam splitter cube to get good centering for that set of fibers. Note that usually the beam splitter cube does not have to be moved and you should investigate other likely causes for the misalignment before moving the cube.
    8. Use small knurled knobs to adjust centering for each APD fiber that doesn't have good centering in the previous step.
    9. Now that all four APD fibers are coaligned, check to see if back propagation hits the face of the red point source fiber (or white light source pinhole if it is at the cassegrain focus).
    10. Steer APD TT stage so that light hits the red point source fiber. Note that the stage is rarely out of alignment and you should only steer it if absolutely necessary.
    11. Recheck back propagation centering for each fiber. If they are all off, use small beam splitter cube to recenter.
    12. Repeat previous two steps until satisfied with alignment.
13. Check centering on slow WFS. If not properly centered, fix and repeat previouis step.
14. Align into IRCAL (pointing and pupil alignment).(see procedure elsewhere)
15. Boresight WFS to IRCAL by fieldsteering (Fast WFS P&C Control) red light source on WFS.
16. Boresight APDs to IRCAL.
    1. See if light hits APDs, if not, use mover to find it. If all else fails, go back to steps 12j-k.
    2. Close TT loop.
    3. See where light hits IRCAL.
    4. Steer APD TT stage (using micrometers) so that red light source (or white light, if that is the source you are using) is well pointed on the WFS and hits right spot on IRCAL (should be the same if did step 14 correctly).
    5. Open TT loop.
17. Change software back to NGS mode.
    1. turn off APDs
    2. turn on NGS TT Drive
    3. Dismiss LGS APD Tip/Tilt window.
18. Focus IRCAL. (see procedure elsewhere)
19. Image Sharpen IRCAL. (see procedure elsewhere).

NGS to LGS on Sky Alignment

This has been updated for the new Renishaw encoded mounts (2004 May 9).

1. Move telescope to either the N or S zenith boresite position.
2. Switch from Mirror to 2nd Dichroic. Make sure that the alignment pinhole behind the 2nd Dichroic is completely open.
3. Move 1st Dichroic, 2nd Dichroic, WFSM and TTCube to zero. Reset all Cums to Zero.
4. Change software to LGS mode (both AO and Telco software)
   1. Change to AO w/ APD guide matrix in Telco.
   2. Push LGS button in CentDiag window.

   The following two steps are optional. In most cases the white light source is too bright to close the TT loop on, even with the ND2 in front of the APD TT sensor.

5. [Optional] Put in the white light source (WLS).
6. [Optional] Check internal strehl with APD TT and AO loops closed. Should be comparable or slightly less than the internal strehl in NGS mode.
7. Change to LGS control matrix (typically we use CMSep03_00wls3 matrix, though if conditions are poor, use the CMSep03_00laser, laserwls, or dimlaer matrices). There will be different hartmannModes for LGS mode, so those should be changed over at this point as well.
8. Make sure radar is on and visual observers are ready.
9. Propagate laser.
10. Focus telescope on laser guide star.
11. Focus laser spot using laser launch telescope optics. Make use of the slic video frame grabber program to measure FWHM of the laser spot during this procedure. The goal is to get the smallest, roundest laser spot possible.
12. Have laser operator steer spot to the boresight position on the guide TV.
13. Send laser light to WFS (make sure WFS is still at NGS focus position!) and have laser operator steer spot to center of WFS. You may have to open iris to 30000 counts or so to give a wider field of view for finding the laser guide star.
14. Close iris to about 5000 counts (depending on conditions you may have to have a smaller or larger iris setting).
15. If necessary, steer iris to clip Rayleigh scattered light. Often the iris doesn't need to be steered at all, or sometimes the iris is already in the correct position if the laser guide star has been used on previous nights. Typical iris position is 1 arcsec North. Once set it should not have to move again for the rest of the night (or run for that matter, unless something bad happens to the system's alignment).
16. Tune laser off wavelength. Take a cflat on the WFS.
17. Tune back on wavelength.
18. Close uplink TT. Confirm that it is working properly. You may want to tune the TT gain (usually we run at a TT gain of 0.5, though we also have run with a gain up to 1.0, if conditions warrant it).
19. Close AO. Confirm that it is working properly. You may want to tune the AO gain for best performance. Usually the best gain is about 0.2 less than the NGS AO gain for a bright star.
20. Open loops and shutter laser.
21. Move telescope to a 9th magnitude star near (closer is better) the first science target (make sure it is cleared by space command). We use this bright star to establish a boresight position for this region of the sky, as well as establish a reference BWFS image for use the rest of the night. This star should be bright enough to easily see on the WFS to assist finding the boresight position for the APDs.
22. Close APD TT loop on the star (you may have to use a some ND in the APD TT sensor). If this is the first night of an LGS run, check to make sure telescope offloading is working correctly.
23. Refocus telescope by moving secondary mirror position until WFS focus reads within +- 1.0. You may have to adjust WFS P&C so that you are well aligned to get a good focus measurement off the WFS. Note that you will probably have to take a new cflat on the WFS to get a good focus measurement on the 9th magnitude star.
24. Close AO loop and check strehl (use the Ks filter in IRCAL and a few second exposure). This strehl is likely to be less than in NGS mode because of using the laser control matrix and using APD TT and AO instead of regular NGS mode.
25. Tune APD TT gain. A typical value is 0.01 (values usually range between 0.01 to 0.001).
26. Take a reference BWFS image. Typical exposure is 10 or 30 seconds.
27. Open loops, mark boresight position on guide TV (bin by 1 mode).
28. Move WFS back to LGS focus using airmass lookup table (using LGSairmass progroam).
29. Propagate laser and boresight on guide TV.
30. Send light to WFS, close APD TT loop on TT star, and steer laser so centered. You will probably have to field steer the 9th magnitude star off the WFS (typical move is 5 arcsec N and 5 arcsec) so that it isn't visible on the WFS.
31. Move iris to clip Rayleigh scatter, if necessasry. This usually isn't necessary because the iris position set a zenith should still apply.
32. Tune off wavelength and take a new WFS cflat.
33. Tune back on wavelength.
34. Close all loops, adjust WFS Centering, and check strehl on IRCAL.
35. Use BWFS measurements to adjust focus position of the WFS.
36. Check strehl on IRCAL.
37. Open all loops.

    The following few steps are optional but particularly recommended for the first night of an LGS run.

38. [Optional]Move to an 11-13th magnitude star near the science target. This star is used to check strehl and do on-sky image sharpening. This is difficult to do with the 9th magnitude star because you have to field steer too far off-axis to get the star off the WFS.
39. [Optional]Close APD TT loop on 11th mag star. You may have to field steer a few arcseconds off-axis to get the 11th mag star off the WFS.
40. [Optional]Propagate laser.
41. [Optional]Do on-sky image sharpening. Typical exposure times are 10 to 20 seconds in the Ks filter. First step is to modify mode 3, typically setting it to zero. Often that is all the image sharpening required.
42. [Optional]Open loops.
43. Move telescope to science target guide star.
44. Close TT loop on guide star.
45. Propagate laser, close uplink TT and AO.
46. Field steer to science target. Remember to open loops before field steering and to close the APD TT loop promptly after the field steer is completed. If the TT star is faint, you may have to TTImage in CentDiag to locate it.
47. Close uplink TT and AO. Adjust WFS centering as necessary.
48. Take science data.

Moving to a new LGS science target

1. Field steer back to zero arcsecond offsets and centering
2. Move telescope to 9th to 11th magnitude star near science target (this does need to be a cleared target by Space Command).
3. Close APD TT loop. Allow telescope to offload.
4. Move WFS to proper position for current airmass.
5. Open APD TT loop and mark position of star on guide TV.
6. Propagate laser and steer to same position as the star.
7. Put laser on WFS (you will probably have to field steer the TT star 5 arcsec N and E to get it off the WFS).
8. Have the laser operator steer the laser on to the WFS.
9. Close all loops. Adjust gains/rates, get new cflat, etc. as necessary.
10. Take BWFS image to check WFS focus position.
11. [Optional] Take image on IRCAL to check strehl.
12. Open all loops.
13. Field steer APD TT star back on axis.
14. Shutter laser. Move telescope to science target TT star.
15. Make sure you see TT star on APDs.
16. Open APD loop. Field steer to science target.
17. Close APD TT loop.
18. Propagate laser.
19. Close loops.
20. Take science data.

Tracking alignment during an LGS exposure

Switching from LGS to NGS mode

1. Switch back to NGS mode software.
2. Load in NGS centroids, control matrix and hartmannModes.
3. Move WFS to NGS focus.
4. Close loops on white light source.
5. Focus spot on IRCAL by moving WFSFocus stage (not IRCamFocus!) (either do a regular focus fit run or use BWFS - 1st choice seems to be more accurate)
6. Go to science target guide star and observe!

Afternoon LGS Alignment Check

1. Exit ircalui, move data using the ircalcopy script, and restart ircalui.
2. Turn on TT 100V, DM 100V, and motor 24V power supplies.
3. Turn on red laser source (RLS).
4. Start APD TT software and turn off T/T Drive.
   -->[with new lgs7 APD code, skip both parts of previous step]
5. Put mirror in E-Null position from the APD TT window.
   -->[with new lgs7 APD code, skip previous step]
6. Take a short exposure on IRCAL (all filters in the Open position) and measure the pixel position of the RLS.
7. If the RLS is not at (or near) the center of IRCAL, first check the IRCAL steering mirror micrometers to make sure one of them hasn't been bumped (proper positions for these mirror micrometers should have been recorded during initial alignment). If these mirror positions are correct, or if after moving them to their proper positions the RLS is still not in the correct position, then move the FiberStage X and Y motors to correctly position the RLS.
8. Turn on APDs. Put APD TT in Open mode. [note: no mover in lgs7 APD mode] Use mover to find the RLS if necessary.
9. Close the APD TT loop on the RLS.
10. Take a short exposure on IRCAL and measure pixel position of RLS.
11. Adjust APD Pointing to get RLS to hit same spot on IRCAL with TT closed as in E-Null.
12. Move WFS to the nominal NGS focus position (typically zero counts on the WFS focus stage).
13. Make sure that you have a current cflat and NGS control matrix for the WFS.
14. Adjust WFS Pointing and Centering (P&C) until RLS well aligned on WFS (this step is commonly called boresighting the WFS). WFS Tip and Tilt readings should be very small, e.g. +-0.05, with APD TT closed.
15. Close AO loop and check Back WFS centering. If centering is way off, try to determine what has moved before adjusting APD Centering (e.g. has just the TT Cube or 1st Dichroic position not close to zero, or has the iris behind the 2nd Dichroic gotten partially closed). If you can find no other source of the problem, you can adjust APD Centering. After adjusting APD Centering, you should back propagate to make sure that you are still properly centered with respect to the APDs. If back propagation shows that everything is off, think long and hard about causes of the misalignment before changing anything that isn't a motorized mount. Odds are the alignment is a motorized mount problem not a manually steered optic. If you decide to move the small beam splitter cube or an individual fiber, be prepared to do all steps of LGS alignment involving the APD TT stage in the main alignment procedure above. This is time consuming and difficult and to be avoided as much as possible during an LGS AO run.
16. If Back WFS centering is acceptable, call the positions of all the field steer motors zero and reset all the cumulative moves in the WFS and APD P&C windows.
17. Switch back to NGS TT mode:
    1. Turn off APDs.
    2. Kill configlgs on lgs3 (if running).
    3. Start configngs on lgs3 (if not already running).
    4. Turn on T/T Drive and TT Offload..
    5. Push NGS button on the PowerUp checklist.
18. Put in White Light Source (WLS).
19. Close loops and check strehl on IRCAL with WLS. Typically this should be done at 500Hz, AO gain of 0.5, and TT gain of 1.0. Typical exposure time of 200ms with 10 coadds using the Br-Gamma filter in IRCAL.
20. Fine focus IRCAL by moving WFS, because that has been moved between NGS and LGS focus during the previous night.
21. Image sharpen on IRCAL.