Inspection of MODS Masks

Inspection of Cut Masks

Masks should be inspected prior to installation in the instrument on the light table with the microscope or any cast off, fibers, or other obscurations. Masks must meet the criteria as described in the Mask Fabrication Document and the Mask Program SPIE 2014 paper, laid out in the following table:

Slit Tolerances MODS
Width 0.15-1.2mm
Length <10mm (typ)
Orientation ±30°
Shape Arbitrary polygon or circle
Width Tolerance ±15um
Position Tolerance ±15um
Edge Roughness ±1.8um RMS over 180um
Inspect each slit of a newly cut mask for cast off, fibers, or other obscurations. If possible, remove the obscuration with dry air, a small tool, pin, or tweezers. Castoff typically comes off with very little effort. If it is not possible to "clean up the slits" or remove the obscuration, the mask may need to be re-cut. Notify SciOps immediately so they can get the ball rolling on getting a new mask re-cut.

Cast off in a slit of a mask as viewed through a microscope on a light table.Light table and microscope used for inspection of freshly cut of masks.
Image 1: Left - Cast off in a mask slit as seen through a microscope on a light table. Right - Microscope and light table in 116 used for inspecting masks.

Once all slits in all masks have been inspected they are ready to be inserted into the instrument. Install the masks following the procedure outlined in the Mask Exchange procedure: (

Running Script

The last step in the MODSMaskExchange procedure is to run the script which takes blue and red images of each mask. This script should have been created using mkMaskSnap on the mods1 or mods2 computer, and, following the procedure in MODSMaskExchange and repeated below, it should have been copied to the obsN computer:
  1. In a terminal logged in to the mods1 or mods2 computer, after you run mkMaskSnap, there should be a file called
  2. Type scp lbto@obs2:/home/lbto/ISp/maskSnaps/ (where 2 is and obs machine number, but could be 3 or 4) to copy to the directory /home/lbto/ISp/maskSnaps/ and rename it to
  3. Logged into an obs machine as lbto, start up MODS1 or MODS2.
    1. Bring up a terminal and start the MODS User Interface by typing: mods1 start gui or, for MODS2, mods2 start gui. A gui like the following will appear:
  4. In the MODS Control Panel, click on the Setup icon on the left sidebar to display the MODS Instrument Setup screen
    1. Click “GetDate” on the right side of the Instrument Setup Screen to update the UT date in the image file names:
      1. If it is before 17:00MST (00UT), the date will be the same as last night's UT and you should click "refresh" to increment the image counter by one, so the mask images will not have the same filenames as any data taken the previous night.
      2. If it is after 17:00MST, then the UT will be the same as that for the following night, and the image counter will be 0001.
      3. Click “Apply” on the right side to store the date and starting index number, and then
    2. On the left side of the Setup Sceen, edit as needed the names of Observer, Support Staff, any comments, and click "Apply" and then "Save".
  5. Bring up a new terminal and open the mods image display, type: modsDisp for MODS1, or mods2Disp for MODS2. This will launch two read-only ds9 windows to display the most recent Blue and Red images.
  6. Bring up a 3rd terminal to run scripts.
    1. Wake mods up:
      1. cd ~modseng/modsScripts/Support/
      2. execMODS --mods1 will wake up MODS1 and execMODS --mods2 will wake up MODS2. (To wake both MODS1 and MODS2 simultaneously, execBinoMODS
      3. Watch the progress on the MODS control panel and in the terminal as it runs. It takes about a minute. Watch for any errors, and make sure the laser turns on at full strength
  7. Run the mask snap.
    1. Make sure that the telescope is at zenith or at a position with elevation 60deg with a PA of 0, and will remain there for the duration of your masksnap. This script should take about 20 minutes if all 12 slots are filled, but less time for fewer masks. You will be asked to confirm this condition is met, but good to make sure before you get started. Open a new terminal and type:
    2. cd /home/lbto/ISp/maskSnaps/
    3. for MODS1, type execMODS --mods1 or for MODS2, execMODS --mods2
      1. Watch the progress. If the script fails with an IMCSlock timeout and "r" does not resolve it, the laser may not be on). The basic troubleshooting in the cookbook treats this, and the Advanced troubleshooting describes better the remedy which is to turn the irlaser off, back on and enable the irlaser (it may not work the first time).
      2. Watch the ds9 displays. Pick a camera, and check the slits as the images stream in. If time allows, slits can be confirmed in the images of slits in the second camera but things do stream by quickly. The Red images will display first with the blue following a few seconds after. Change the stretch and scale so that the slits are well defined. Check that the number etched in the mask matched the number title assigned to the ds9 image. This confirms that updateSlits was run correctly and the masks are in the correct positions. If any signs of debris or castoff is found, record the image number, rough location of the obscuration, and mask ID. All images can be found in /newdata and reviewed in more detail with more time after the script has completed.
      3. Any masks noted to have debris or cast off will have to be pulled and fixed following the mask exchange procedures and inspected on a light table.
  8. Put MODS to Sleep when done.
    1. cd ~modseng/modsScripts/Support/
    2. execMODS --mods1 for MODS1, or execMODS --mods2 for MODS2. Once mods is put to sleep, all windows and GUIs for mods can be exited and closed.
The full mods mask inspection procedure is outlined in CAN Document 010s012: Procedure for inspection of Newly Cut MODS Masks

-- %USERSIG{JenniferPower - 2014-09-21}%



I Attachment Action Size Date Who Comment
MODS_Mask_Fabrication_Requirements_R2.pdfpdf MODS_Mask_Fabrication_Requirements_R2.pdf manage 114 K 01 Oct 2014 - 23:19 JenniferPower MODS Mask Fabrication Requirements R2.pdf
Mask_Program_SPIE_2014_final_rev.1_140603.pdfpdf Mask_Program_SPIE_2014_final_rev.1_140603.pdf manage 901 K 02 Oct 2014 - 20:26 JenniferPower Mask Program_SPIE_2014
Topic revision: r16 - 16 Nov 2016, OlgaKuhn
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