[Halld-tagger] interesting result just back from Applied Diamond

[Richard Jones]

Dear colleagues,

We have produced a new 7mm diamond sample using laser ablation, but this
time instead of ablating it down to the final thickness we stopped at 40
microns. We then shipped it off to Applied Diamond for them to etch it, and
they took off a final 20 microns for a finished (inner membrane) thickness
close to 20 microns.

When we first looked at it we thought it was cracked, but after discussions
with Advanced Diamond engineers we understand that the hairline we saw was
just a surface artifact from the apparatus that was used to hold the
diamond during the etching. The results look amazing. See the attached
photograph. This is in sharp contrast with what we installed in the
goniometer back in February, which look black in the inner region due to
carbon residue. The bright square in the upper right corner of the images
is just a reflection from the camera flash.

We plan to look at it under a scanning electron microscope to see if there
were any micro-pores or cracks created by the etching process, but with an
optical microscope it looks as smooth as it did when we finished with the
laser. I have written to our collaborator Ken Finkelstein to ask if we
might get a few hours for a quick measurement of the rocking curve on this
sample. I believe we will see a huge improvement over the un-etched samples
JD70-118 and JD70-119.

-Richard Jones
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