By Claire Hansel
SLAC/University of Colorado Boulder
+1 (207) 749-7461
This procedure explains to clueless grad students how to mount electro optic crystals for EOS-BPM as in Figure 1. This document may change as the EOS-BPM crystal holders are redesigned in the future.
Required:
Crystals (Red = ZnTe, Yellow = GaP)
Crystal Mounts (can reuse old mounts if needed)
Torr seal gun and cartridge (Should be in the chemical cabinet)
Metal Inverse Tweezers (Fig 3)
Plastic normal tweezers (Fig 4)
Paperclip
Rubber Band
Kapton tape
RS Spacer Kit
Small water tight basin to soak the Torr seal cartridge
Vacuum Foil, Gloves, Allen Keys, Kim Wipes, Ethanol
Step 1:
Remove the correct EOS-BPM parts from the PB and bring them up to 244. For the EOS1/Closer/Southern crystal you can take off the whole S-mount (Fig 2) including the mirrors. For the EOS2/Further/Northern crystal you can take just the crystal holder.
Step 2:
Fill up the basin with hot water from the sink in the bathroom and soak the Torr seal cartridge for ~20 minutes to decrystalize the epoxy. You can do the next steps while waiting.
Step 3:
Make a torr seal applicator by unfolding the paperclip and wrapping Kapton tape around one end.
Step 4:
Put a rubber band around the metal inverse tweezers (Fig 3) until the equilibrium separation of the tweezer tips is just less than the crystal edge size.
Step 5:
Get a mount. If not using a new mount, break off the old crystal and put it in the broken crystals box and use wire cutters to scrape off any remaining crystal and epoxy. Then wipe the mount down with ethanol.
Step 6:
Make a crystal rest (Fig 5) by stacking RS Spacers to the right height and then putting Kapton tape on the top. The purpose of this is so that the crystal is level with one end on the mount and one end on the crystal rest while the epoxy is curing.
Step 7:
When the epoxy cartridge is done, dry it, attach it to the gun, and remove the cap. Make a small throwaway puddle on the foil to get out any epoxy that may have touched water and verify epoxy comes out of both tubes. If it doesn’t come out of a tube you have to poke the opening with the non-Kapton side of the torr seal applicator.
Step 8:
Prepare to pick up the crystal. Remember they are expensive and very fragile, especially the thin ones. This procedure worked with a 100um thick crystal but you may have to . I recommend practicing handling a broken crystal first to get a sense of the fragility. Make sure the crystal box is close to the crystal rest so you don’t have to move it far. The crystal should have two cut corners which, if the crystal is 110 cut, are parallel to the [-1, 1, 0] axis (See Figure 6). Make sure you put epoxy on the correct position (left or right) of the mount depending on whether you're mounting EOS1 or EOS2 so that the laser goes through the crystal.
Step 9:
Make a puddle of epoxy on the foil and mix it up with the applicator. Use the applicator to put a small amount on mount. Move the mount close to the spacer support but don’t epoxy the mount to it. Carefully pick up the crystal with the metal inverse tweezers and making sure it has the correct orientation move it above the correct location and drop it into place on the epoxied mount. Use the plastic tweezers to gently push the crystal down and then into the mount.
Step 10:
Put a plastic box over the whole thing so it’s not disturbed and wait one day.
Step 11:
Re-assemble EOS and install in the tunnel. Celebrate your success!
Figure 1: Mounted GaP Crystal
Figure 2: EOS S-Mount
Figure 3: Metal Tweezers (with Rubber Band)
Figure 4: Plastic Tweezers
Figure 5: Crystal Rest with Crystal Curing on it
Figure 6: Crystal Orientation Diagram (Note: this diagram is based on what the manufacturer told us and we haven't verified the orientation in the lab with a THz source)
