LGS Alignment Procedures

AO LGS Optical Alignment
Start of Night Focus and Tuning Procedure
NGS science target setup
NGS to LGS on Sky Alignment
Moving to a new LGS science target
Tracking alignment during an LGS exposure
Switching from LGS to NGS mode
Afternoon LGS Alignment Check

AO LGS Optical Alignment

AO Alignment for LGS Mode (Assumes currently reasonably aligned for NGS mode)

NOTE: This procedure is typically done in the lab and should not normally be necessary during regular telescope operations. For regular operations refer to Daily Afternoon LGS Alignment below.

  1. Install 600nm dichroic instead of mirror in 2nd dichroic mount.
  2. Put in alignment laser (remove initial turning mirror if it is installed).
  3. Align through all pinholes with alignment laser.

    NOTE: The following 2 steps don't need to be done when mounting AO on the telescope unless you suspect something has drastically changed since the alignment was done in the lab.

  4. Coarse align to IRCAL (hit target on IRCAL dark cover). Note that this should not be necessary if the NGS alignment was good.
  5. 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.
  6. Put in red light point source.
  7. If doing a full alignment in the lab:
    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 couple pixels is sufficient.
  8. If doing initial optical alignment on the telescope:
    Move FiberStage X and Y so that the red light point source is centered on IRCAL (pixel 128,128). There is a script on ircalbox called rlsPosition.tcl that automates most of this procedure.
  9. 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

  10. Put into LGS mode by clicking LGS button in CentDiag GUI.
  11. Check centering on slow WFS. If not properly centered, fix and repeat previouis step.
  12. Done in lab only, not on telescope. Align into IRCAL (pointing and pupil alignment).(see procedure elsewhere)
  13. Done on telescope initial alignment. Align into IRCAL. Use rlsPosition script in ircalui software to position RLS to center of IRCAL.
  14. Boresight LTT to IRCAL.
    1. Turn off RLS and acquire a new background for the LTT camera.
    2. Turn on RLS.
    3. Close LTT loop.
    4. See where light hits IRCAL.
    5. Use LTT P&C GUI to adjust pointing of LTT so that RLS is at pixel 128,128 on IRCAL.
    6. Check centering on Slow WFS camera.
  15. Boresight WFS to LTTs and IRCAL by fieldsteering (Fast WFS P&C Control) red light source on WFS. Tip and Tilt readings on CentDiag should be as close to zero as possible (less than +/- 0.01). Centering should have outer subapertures as evenly illuminated as possible.
  16. Change software back to NGS mode by clicking NGS button in CentDiag GUI.
  17. Put in White Light Source (WLS).
  18. Focus IRCAL. (see procedure elsewhere)
  19. Image Sharpen IRCAL. (see procedure elsewhere).

Start of Night Focus & Loop Tuning

During twilight the AO operator should focus the telescope and tune the AO loop gains to maximize AO performance.

  1. Point to a bright star (about 6th magnitude) near zenith and get it on the WFS. You may have to open the iris to 35000 or 45000 counts and decrease the AO rate if it is the first night of an AO run and the boresight position on the guide camera hasn't yet been established.
  2. Move telescope 30 arcsec and get a cflat at 500 Hz for the WFS.
  3. Move telescope back to star and close TT Loop.
  4. Focus telescope so that focus number in centDiag is very close to zero.
  5. Close AO loop.
  6. Adjust TurningMirror X and Y to adjust WFS centering.
  7. Tell Telescope Tech that star is centered. Open loops and have telescope tech mark a zenith boresight position on the guider.
  8. Get the light back and close the TT and AO loops.
  9. Take WFS Data. Put the appropriate file date/number code for closed loop data in the aoidl GUI (type aoidl at the idl prompt to start the GUI).
  10. Make a new mirror flat (mflat in centDiag GUI).
  11. Open AO loop (leave TT loop closed).
  12. Flatten DM (push Flatten button in centDiag GUI).
  13. Take WFS Data. Put the appropriate file date/number code for open loop data in the aoidl GUI.
  14. Click R0 Calculator button in aoidl. R0 measurement might be bad if over driving the system (i.e. gain is too high).
  15. Click Power Spectra button in aoidl. Evaluate power spectra and adjust AO and TT loop gains appropriately.
  16. Take more closed and open loop WFS data as necessary to tune AO system performance. You probably also want to take short (e.g. 1 to 3 second total integraion time) exposures on IRCAL with the Br-Gamma filter to help evaluate system performance.
  17. When finished, open loops and move to first science target.

NGS science target setup

This procedure describes the steps required for setting up on an NGS science target after doing the beginning of
Night Focusing & Loop Tuning.
  1. Point to the NGS tip/tilt star. Use the Telescope Move window to fine tune pointing (pixel scale on WFS is 2 arcsec pixel, North is to the left and East down on the WFS monitor).
  2. Get a fresh sky background: Move telescope 20 arcsec North and push the Cflat button in the CentDiag window. Move 20 arcsec South.
  3. Close the TT Loop (Loop Control window).
  4. Examine the counts per subaperture in CentDiag. If less than 100 or 150, go to a slower AO rate. If more than ~20,000 the camera saturates, so you need a faster AO rate and/or ND filter. Rates are set in the AO Loop Parameters window. Filters are the WFS ND filters in the first column of the Filter Wheels GUI. (Note: when running at 1000 Hz rate, you should reduce the TT gain to .5 or less, otherwise the loop gets unstable).
  5. If you change the AO rate or WFS filter, you need to acquire a new Cflat for the WFS camera. (offset the telescope 20" North, push the Cflat button, move telescope 20" South).
  6. Close the TT Loop.
  7. Close the AO Loop.
  8. Adjust centering (right panel of the Fast WFS P&C Control window). Brightness of the spots in the top and bottom rows should be about equal. Same is true for the left and rightmost rows. If it is not balanced, do centering steps of ~20 counts in the direction you need to move photons (e.g. if the top spots are less bright than the bottom spots, do a centering move of 20 counts up).
  9. When centering is done, advise the observers that they may take data.
  10. If the science target is off-axis, have the observer field steer (using the IRCAL WFS Steering/Nodding Control window) to the science target. After closing the loops on the star, you may have to adjust centering again before the observer takes data.

NGS to LGS on Sky Alignment

This procedure describes the various necessary alignment step for switching to LGS mode after observing in NGS mode the first part of the night.

This has been updated 2009 June 10.

  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. Field Steer WFS and LTT motors to zero.
  4. Change software to LGS mode by pushing LGS button in CentDiag window.
  5. 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 may be different hartmannModes for LGS mode, so those should be changed over at this point as well.
  6. Load proper target into the Laser Shutdown Monitor software.
  7. Make sure radar is on and visual observers are ready.
  8. Propagate laser.
  9. Focus telescope on laser guide star. (Note: It is good to record the NGS telescope focus. Telescope focus for the sodium layer is about 15 POCO focus counts higher than NGS focus).
  10. Focus laser spot using laser launch telescope optics. The goal is to get the smallest, roundest laser spot possible.
  11. Have laser operator steer spot to the boresight position on the guide TV.
  12. 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.
  13. Close iris to about 8000 counts (depending on conditions you may have to use a smaller or larger iris setting).
  14. 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).
  15. Tune laser off wavelength. Take a cflat on the WFS.
  16. Tune laser back on wavelength.
  17. Close uplink TT. Confirm that it is working properly. You may want to tune the TT gain (often we run at a TT gain of 0.8, though we also have run with a gain up to 1.0, if conditions warrant it).
  18. Close AO. Confirm that it is working properly. You may want to tune the AO gain for best performance.
  19. Take WFS Data. Record date, data file number, frame rate, etc. in user@gouda:~/observers/lgs/LGSPowerReturn.txt. Measure intensity (enter WFS data date/number into aoidl and push Intensity button or, from the idl command line, e.g., IDL> inten,'/net/lgs7/home/winkerbean/AO/Data/RunData/070722/inten_006').
  20. Open loops and shutter laser. Get power reading of laser from laser operator and record in LGSPowerReturn.txt.
  21. Move telescope to a 9th magnitude star near (closer is better) the first science target (make sure it is cleared by space command). [Note: 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 be easily seen on the WFS to assist finding the boresight position for the LTT sensor.]
  22. Load 9th mag star lsm file into Laser Shutdown Monitor.
  23. Return to the NGS POCO focus position.
  24. Get new cflat for WFS and background for LTT camera.
  25. Close LTT loop on the star. If this is the first night of an LGS run, check to make sure telescope offloading is working correctly. If offloading is not working make sure olon button is pressed in centDiag. If it still doesn't work, restart on shard: /usr/local/lick/etc/init.d/ restart
  26. 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 LTT and AO instead of regular NGS mode.
  27. Tune LTT gain. A typical value is 0.1 (values usually range between 0.05 to 0.15).
  28. Take a reference BWFS image. Typical exposure is 5 or 10 seconds. Useful commands for BWFS camera:
    • newbaseline
    • setrois,/pick (if first night of run or otherwise necessary)
    • anal,baseroi=roi0,theroi=roi,cor=cor
  29. Open loops, mark boresight position on guide TV.
  30. Move WFS back to LGS focus. To get the predicted value at the current telescope position, click on WFSFocus Track in the WFSFocus Tracking GUI. [You can also use ~/observers/lgs/tcl/LGSairmass1 to calculate the position].
  31. Propagate laser and boresight on guide TV.
  32. Send light to WFS, close LTT loop on TT star, and steer laser so it is centered. Use the narrowband sodium filter to block light from the star if necessary. If the sodium filter is not installed for some reason, you may have to field steer the star off the WFS (typical move is 5 arcsec N and 5 arcsec E).
  33. If necessary, move iris (with Iris Position GUI) to clip Rayleigh scatter. This usually isn't necessary because the iris position set a zenith should still apply.
  34. Tune off wavelength and take a new WFS cflat.
  35. Tune back on wavelength.
  36. Close all loops, adjust WFS Centering, and [optional] check strehl on IRCAL.
  37. Use BWFS measurements to adjust focus position of the WFS.
  38. Turn on WFSFocus tracking.
  39. Check strehl on IRCAL.
  40. [Optional] Do on-sky image sharpening.
  41. Open all loops.
  42. Shutter laser.
  43. Move telescope to science target guide star.
  44. Load science target lsm file into Laser Shutdown Monitor GUI.
  45. Close LTT loop on guide star.
  46. Propagate laser, close uplink TT and AO.
  47. Field steer to science target if off-axis guide star.
  48. Close uplink TT and AO. Adjust WFS centering as necessary.
  49. Take science data.

Moving to a new LGS science target

  1. Open loops and shutter laser.
  2. Field steer back to zero arcsecond offsets and centering.
  3. If going to a new region of the sky (e.g. big telescope move):
    1. Move telescope to 9th magnitude star near science target (this does need to be a cleared target by Space Command).
    2. Load the star's LSM file into IRCAL's laser shutdown monitor GUI.
    3. Close LTT loop. Allow telescope to offload.
    4. Open LTT loop and mark position of star on guide TV.
    5. Propagate laser and steer to same position as the marked boresight (i.e., the 9th mag star).
    6. Put laser on WFS (you need to use sodium filter to block the TT star light).
    7. Have the laser operator steer the laser on to the WFS.
    8. Close all loops. Adjust gains/rates, get new cflat, etc. as necessary.
    9. Take BWFS image to check WFS focus position.
    10. [Optional] Take image on IRCAL to check strehl.
    11. Open all loops.
    12. Shutter laser.
  4. Move telescope to science target TT star.
  5. Close LTT loop (adjust rate and get new background as needed).
  6. Load targets LSM file into the laser shutdown monitor GUI.
  7. Propagate laser and close TT and AO loops.
  8. Field steer to science target.
  9. Take science data.

Tracking alignment during an LGS exposure

Periodically, both WFS pointing and centering need to be checked, as well as the WFS focus position. WFS pointing and centering should be checked and adjusted between (but not during) exposures. The frequency of these corrections depends upon the frequency of dithers as well as the laser brightness and Rayleigh scatter. WFS focus tracking is now automated in the WFSFocus Tracking GUI.

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. If necessary or desired, replace 2nd dichroic with the mirror.
  5. Go to science target guide star and observe!

Daily Afternoon LGS Alignment Check

Every afternoon some basic alignment should be checked and tweeked so that we get the best performance possible out of the AO system.
  1. Check read noise level on IRCAL.
    • Make sure IRCAL darks from previous night completed successfully.
    • Enable AO Communications and Sounds in ircalui Config menu.
    • Move IRCAL filters to the dark position.
    • Take 2 exposures of 1000ms x 1 coadd x 16 reads, and subtract them from each other. Standard deviation should be < 3DN.
  2. Turn on red laser source (RLS).
  3. If things are in a decent state you will see hartmann spots on the WFS.
  4. Turn off Offloading (oloff) in CentDiag.
  5. Turn on 100V DM power and 24V motor power if they aren't already on.
  6. Make sure the following motors are in POS mode, click on Actions - Enable motion in the AO motor control GUI.
    • Fiber X & Y
    • 1st Dichroic X & Y
    • 2nd Dichroic X & Y
    • WFSM X & Y
    • TTCube X & Y
    • Iris Close
    • WFS Focus
    • IRCam Focus
    All the above motors should have a green check mark by them.
  7. Set the following motors to 0 position. (This is most easily done by clicking "Red Source" in the Fiber Source Selection window and clicking "Go to Zero" in the LGS Tip/Tilt P&C window).
    • Fiber X & Y
    • 1st Dichroic X & Y
    • 2nd Dichroic X & Y
    • WFSM X & Y
    • TTCube X & Y
  8. Set RLS position.
    • Take a short exposure (57 or 100 ms with 10 coadds is typical) with IRCAL (all filters in the Open position) and make sure RLS is in the central region of the chip. If it isn't, move Fiber X and Y stages so that it is.
    • Use rlsPosition script in ircalui to place RLS at the center of the array.
    • "Assert Zero" for Fiber X and Y stages.
  9. Switch to LGS mode in CentDiag GUI.
  10. Set LTT and WFS to 500 Hz
  11. Turn on RLS and install ND filter in WFS and LTT camera if RLS is too bright. Too bright (with good cflat) for the WFS is generally >20000 counts per subap, for the LTT >8000 counts per subap.
  12. Turn off RLS and get background for LTT and WFS (cflat).
  13. Turn on RLS.
  14. Close the LTT loop on the RLS (if RLS is not close enough to center, use LGS Pointing GUI to get it close).
  15. Take a short exposure on IRCAL and measure pixel position of RLS.
  16. Adjust LTT Pointing with the lttPosition script.
  17. Move WFS to the nominal NGS focus position (Renishaw encoder at zero) if it isn't already there.
  18. Make sure that you have NGS control matrix (currently CMSep03_00) for the WFS.
  19. 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. +-0.1 or better, with LTT closed.
  20. Close AO loop and check Back WFS centering. If it is not properly centered, use LTT centering. You will have to open the AO loop and iterate between LTT pointing and centering to get everything properly aligned. You will also have to redo WFS P&C after adjusting LTT pointing and centering.
  21. If Back WFS centering is acceptable,
    • "Assert Zero" for the field steering motors (1stDichroic, 2ndDichroic, WFSM, and TTCube).
    • Reset all the cumulative moves in the WFS and LTT P&C windows.
  22. Open AO and LTT loops.
  23. Switch back to NGS TT mode by pushing NGS button in CentDiag GUI.
  24. Put in White Light Source (WLS). Optional: Adjust position of WLS using Fiber X and Y motors so that tip and tilt are < +/- 0.1.
  25. Remove all ND from WFS and LTT if any were installed. Get new cflat for WFS and background for LTT.
  26. 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 0.5. Typical exposure time of 100ms with 10 coadds using the Br-Gamma filter in IRCAL (check to make sure you aren't saturating in a single co-add and adjust exposure as needed).
  27. Focus and Image sharpen IRCAL. This can be done using the imagesharpen script in ircalui.
  28. "Assert Zero" for the IRCamFocus stage.
  29. Save NGS Hartmann Modes.
  30. Make new mirror sharp file (msharp in centDiag GUI).
  31. Open AO and TT loops.
  32. If AO is in the lab and not on the telescope, put the RLS in and stop here. If AO is on telescope do the following steps.
  33. Move fiber "Out of Way" using Calibration Source GUI.
  34. Turn on Offloading (olon) in centDiag.
  35. Process US Space Command laser shutdown lists (see LGS Target Lists for details).
  36. Exit data taker and restart on karnak for observer if not running the data taker inside a VNC session. If running in a VNC session, make sure the VNC window is on both gouda and karnak.

Elinor Gates
Last modified: Mon Jul 9 10:41:19 PDT 2012